Bug 871569. Re-enable skia on mac.

This was disabled by the layers refactoring (bug 825928)
because of a linking file limit problem.

--HG--
rename : content/html/content/test/test_video_wakelock.html => content/html/content/test/test_audio_wakelock.html
rename : content/html/content/test/wakelock.ogv => content/media/test/bug520908.ogv
rename : content/media/webaudio/test/test_audioBufferSourceNodeGain.html => content/media/webaudio/test/test_audioBufferSourceNode.html
rename : layout/mathml/nsMathMLSelectedFrame.cpp => layout/mathml/nsMathMLmactionFrame.cpp
rename : layout/mathml/nsMathMLSelectedFrame.h => layout/mathml/nsMathMLmactionFrame.h
rename : dom/imptests/html/html/dom/elements/global-attributes/dir_auto-contained-dir-L-ref.html => layout/reftests/bidi/dirAuto/dir_auto-contained-dir-L-ref.html
rename : dom/imptests/html/html/dom/elements/global-attributes/dir_auto-contained-dir-R-ref.html => layout/reftests/bidi/dirAuto/dir_auto-contained-dir-R-ref.html
extra : rebase_source : 62515ae689950ac2944c594e096048b957d5183a