I searched a bit and found this helpful article. Here are the most relevant quotes:

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Android 3.0 Honeycomb gave developers the ability to turn on hardware acceleration, but it wasn’t toggled by default.
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According to Romain Guy and Chet Haase (Android engineers):

“With this new pipeline, all drawing operations performed by the UI toolkit are carried out using the GPU. You’ll be happy to hear that Android 4.0, Ice Cream Sandwich, brings an improved version of the hardware-accelerated 2D rendering pipeline to phones, starting with Galaxy Nexus. In Android 4.0 (API level 14), hardware acceleration, for the first time, is on by default for all applications.”