Bug 903949 (part 1) - ChildMemoryReporter should return mProcess in GetProcess() rather than an empty string.  r=jlebar.

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extra : rebase_source : a0979780a7289429e4c06dce2de06576bb3a3e90
Bug 903949 (part 2) - Don't trigger about:memory re-generation when a child process closes.  r=jlebar.

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extra : rebase_source : ee532ba1176906a69cf68774d755856581e44dd9