Work around StateListDrawable padding in search suggestions

Sometimes when searching, some of the suggestions had no left padding.
The left-hand side icons were flush with the left edge of the screen.
The problems was that setting a StateListDrawable as a background
will always set the padding of a View, because of a problem in
DrawableContainer.

DrawableContainer.DrawableContainerState.getConstantPadding()
will always return a Rect if mVariablePadding is false, which
makes DrawableContainer.getPadding() return true, which
causes View to change the padding.

As a workaround, we use setVariablePadding(true) on the background
that we create.

Fixes http://b/editIssue?id=1984813