Bug 1013647. Cache the current context on B2G. r=jgilbert

This avoids the call to EGLGetCurrentContext() which calls
EGLGetError which can be expensive.

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extra : rebase_source : 7d64a1337cbe951069648422d4c42600fdab28a1
Bug 1018416. Add Transform method to nsRegion. r=BenWa

Replace the open coded version with one that avoids
allocation and is O(n*log(n)) instead of O(n*2)

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extra : rebase_source : 9d8de6089bc9fa74ba4b60c3eb3ccf3b3235ad54