Bug 829557. Part 1: When calling into plugin code, identify situations where it is safe (or unsafe) to reenter Gecko from plugin code. r=bsmedberg
When Gecko is reentered from unsafe call sites, we allow the reentry, but we
suppress execution of the refresh driver to minimize the danger.
In this patch, we treat all sites as unsafe.

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extra : rebase_source : 0730f41c9158c868ed4ffcba74ff77abbfebc2cd
Bug 829557. Part 2: Allow plugin code to reenter Gecko safely while while the plugin is processing an input event. r=bsmedberg
When nsPluginInstanceOwner passes input events to the plugin instance,
it's safe to reenter Gecko from plugin code and do anything, even
arbitrary script execution.

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extra : rebase_source : 815683c3027b906c4744495e8e1cfdb261e0c557
Bug 845526. Limit complexity of invalid region in RemoveFrameFromLayerManager. r=mattwoodrow

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extra : rebase_source : ca0a1d7928c991604d5979bcf35b4fcea462c31a
Bug 843214. Make SourceMediaStream::AddTrack/AppendToTrack/HaveEnoughBuffered/DispatchWhenNotEnoughBuffered/EndTrack smoothly handle cases where track does not exist. r=jesup

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extra : rebase_source : adcfa0e92b5e498c597e16e013fdcba2dae4b8e5