ShapedButton uses saveLayer() (and an equivalent technique in pre-HC) to draw our tabs button and back button. saveLayer() is a rather expensive operation and it doesn't seem to be necessary for our needs. The right thing to do here is to simply draw the shapes with colors that respond to the view's drawable state (pressed, checked, etc) where possible. Still have to figure out how such change would interact with our lightweight themes support but it shouldn't be too complicated.
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