Bug 859657 (part 1) - Don't measure MEMORY_EXPLICIT in telemetry because it can cause pauses.  r=jlebar.

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extra : rebase_source : 93a9d3896ec62d54ccfdaa6a8a90a5e9188fe67c
Bug 859657 (part 2) - Remove nsIMemoryMultiReporter.explicitNonHeap because it's more trouble than it's worth;  also remove the "explicit" single reporter.  r=jlebar.

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extra : rebase_source : a146536a3dd0043082bcb1c26d980c4c6d4c0730
Bug 859657 (follow-up) - Bustage fix for opt builds on a CLOSED TREE.  r=me.