Bug 939276 - Use a single GLContext for all SkiaGL canvases r=vlad,gwright,bjacob

--HG--
rename : gfx/gl/GLContextSkia.cpp => gfx/gl/SkiaGLGlue.cpp
extra : rebase_source : 8e85dd34a67c2e193480e9f1f5baf68a898790fe
Bug 970199 - Switch mouse event button type from ushort to short according to spec change. r=smaug

--HG--
extra : rebase_source : 7da22cbb4a3fcc6fa7cc8350bea0f87adf896788