Bug 826521 (part 1) - Add SizeOfIncludingThisEvenIfShared() for strings.  r=bz.

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extra : rebase_source : 5c10fc346ba0c5fa76d947a97254e9ebc49353e1
Bug 826521 (part 2) - Report memory used by event targets, especially XHRs.  r=bz.

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extra : rebase_source : 543f0e367ce73477d62eca544137a101108a97be