How to create standard Borderless buttons (like in the design guideline mentioned)?

Question

To clear some confusion:

This is done in 2 steps: Setting the button background attribute to android:attr/selectableItemBackground creates you a button with feedback but no background.

android:background="?android:attr/selectableItemBackground"

The line to divide the borderless button from the rest of you layout is done by a view with the background android:attr/dividerVertical

android:background="?android:attr/dividerVertical"

For a better understanding here is a layout for a OK / Cancel borderless button combination at the bottom of your screen (like in the right picture above).

<RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:layout_alignParentBottom="true">
        <View
            android:layout_width="match_parent"
            android:layout_height="1dip"
            android:layout_marginLeft="4dip"
            android:layout_marginRight="4dip"
            android:background="?android:attr/dividerVertical"
            android:layout_alignParentTop="true"/>
        <View
            android:id="@+id/ViewColorPickerHelper"
            android:layout_width="1dip"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_alignParentBottom="true"
            android:layout_marginBottom="4dip"
            android:layout_marginTop="4dip"
            android:background="?android:attr/dividerVertical" 
            android:layout_centerHorizontal="true"/>
        <Button
            android:id="@+id/BtnColorPickerCancel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:layout_toLeftOf="@id/ViewColorPickerHelper"
            android:background="?android:attr/selectableItemBackground"
            android:text="@android:string/cancel" 
            android:layout_alignParentBottom="true"/>
        <Button
            android:id="@+id/BtnColorPickerOk"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_alignParentRight="true"
            android:layout_alignParentTop="true"
            android:background="?android:attr/selectableItemBackground"
            android:text="@android:string/ok" 
            android:layout_alignParentBottom="true" 
            android:layout_toRightOf="@id/ViewColorPickerHelper"/>
    </RelativeLayout>

Simply add the following style attribute in your Button tag:

    style="?android:attr/borderlessButtonStyle"

source: http://developer.android.com/guide/topics/ui/controls/button.html#Borderless

Then you can add dividers as in Karl's answer.

Late answer, but many views. As APIs < 11 ain't dead yet, for those interested here is a trick.

Let your container have the desired color (may be transparent). Then give your buttons a selector with default transparent color, and some color when pressed. That way you'll have a transparent button, but will change color when pressed (like holo's). You can also add some animation (like holo's). The selector should be something like this:

res/drawable/selector_transparent_button.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" 
          android:exitFadeDuration="@android:integer/config_shortAnimTime">
     <item android:state_pressed="true"
         android:drawable="@color/blue" />

   <item android:drawable="@color/transparent" />
</selector>

And the button should have android:background="@drawable/selector_transparent_button"

PS: let you container have the dividers (android:divider='@android:drawable/... for API < 11)

PS [Newbies]: you should define those colors in values/colors.xml

For the one who want borderless buttons but still animated when clicked. Add this in the button.

style="?android:attr/borderlessButtonStyle"

If you wanted a divider / line between them. Add this in the linear layout.

style="?android:buttonBarStyle"

Summary

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:orientation="horizontal"
   style="?android:buttonBarStyle">

    <Button
        android:id="@+id/add"
        android:layout_weight="1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/add_dialog" 
        style="?android:attr/borderlessButtonStyle"
        />

    <Button
        android:id="@+id/cancel"
        android:layout_weight="1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/cancel_dialog" 
        style="?android:attr/borderlessButtonStyle"
        />

</LinearLayout>

For material style add style="@style/Widget.AppCompat.Button.Borderless" when using the AppCompat library.

From the iosched app source I came up with this ButtonBar class:

/**
 * An extremely simple {@link LinearLayout} descendant that simply reverses the 
 * order of its child views on Android 4.0+. The reason for this is that on 
 * Android 4.0+, negative buttons should be shown to the left of positive buttons.
 */
public class ButtonBar extends LinearLayout {

    public ButtonBar(Context context) {
        super(context);
    }

    public ButtonBar(Context context, AttributeSet attributes) {
        super(context, attributes);
    }

    public ButtonBar(Context context, AttributeSet attributes, int def_style) {
        super(context, attributes, def_style);
    }

    @Override
    public View getChildAt(int index) {
        if (_has_ics)
            // Flip the buttons so that "OK | Cancel" becomes "Cancel | OK" on ICS
            return super.getChildAt(getChildCount() - 1 - index);

        return super.getChildAt(index);
    }

    private final static boolean _has_ics = Build.VERSION.SDK_INT >= 
                                        Build.VERSION_CODES.ICE_CREAM_SANDWICH;
}

This will be the LinearLayout that the "OK" and "Cancel" buttons go into, and will handle putting them in the appropriate order. Then put this in the layout you want the buttons in:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:divider="?android:attr/dividerHorizontal"
          android:orientation="vertical"
          android:showDividers="middle">
    <!--- A view, this approach only works with a single view here -->
    <your.package.ButtonBar style="?android:attr/buttonBarStyle"
        android:id="@+id/buttons"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:weightSum="1.0">
        <Button style="?android:attr/buttonBarButtonStyle"
            android:id="@+id/ok_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="0.5"
            android:text="@string/ok_button" />
        <Button style="?android:attr/buttonBarButtonStyle"
            android:id="@+id/cancel_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="0.5"
            android:text="@string/cancel_button" />
    </your.package.ButtonBar>
</LinearLayout>

This gives you the look of the dialog with borderless buttons. You can find these attributes in the res in the framework. buttonBarStyle does the vertical divider and padding. buttonBarButtonStyle is set as borderlessButtonStyle for Holo theme, but I believe this should be the most robust way for displaying it as the framework wants to display it.