Bug 1003893 - Ensure that the delete of RasterImage occurs on the main thread. r=seth, a=sylvestre

Dispatch nsRefPtr<RasterImage> to the main thread by NS_ProxyRelease
to avoid RasterImage from being destructed by the DecodeJob thread.
(If gMultithreadedDecoding is true.)
Therefore, DiscardTracker can safely access RasterImage::Discard()
by the raw pointer in DiscardTracker::Node.

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extra : transplant_source : 0%60%E6%86/%15%3D%E5%00%F7eYb%B7%DA%92%5E%C0%3Ex
Bug 1026003 - UI telemetry for opening pages in new tabs from web content contextmenu r=liuche, a=sylvestre

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extra : transplant_source : %12%23%93%DEF%9C%C3%8D%60%F8%C0%EB%FE%F6%E4%18%EE%B2C%19
Bug 1018430 - UI telemetry actions for web page context menu r=liuche, a=sylvestre

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extra : transplant_source : %82%3Du%09%BF%7BH%C3%9D%EB%2CT%06%1D%1E%96%E3%29%FBI
b=1026325 backout 169de60f0b1e from bug 821062 for shutdown hang, a=sylvestre

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extra : transplant_source : %86%FA%A9%7C%0D%D6%BF%24_so%0E%9F%D3%0D%11%DD%FE%C5%EC