the core screenshot function now can capture the screen at any lower resolution
performing bilinear filtering.
we also now have some client code to interface with the screenshot service.
it's now possible to request a screenshot at a lower resolution.
Change-Id: I33689bba98507ab928d0898b21596d0d2fe4b953
screenshots are taken using ISurfaceComposer::captureScreen() which returns
the size of the screenshot and an IMemoryHeap containing the data.
screenshots have limitations:
- they will always fail if a secure window is up on screen
- require GL_OES_framebuffer_object extension
- in some situation, video planes won't been captured
Change-Id: I741c68a2d2984fb139039301c3349e6780e2cd58
