Bug 1076910 - Don't use gfxPlatform::GetPlatform() off the main thread. r=Bas, a=sledru

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branch : GECKO331_2014103013_RELBRANCH
Bug 1076910 - Add some error checks to gfxUtils::EncodeSourceSurface. r=Bas, a=sledru

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branch : GECKO331_2014103013_RELBRANCH