Bug 867757 - Part 1: Allow markers to carry payload. r=aklotz

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extra : rebase_source : 31904aa5f084283bfc23ecfc53762d275967e34b
Bug 918581 - Extend merge-profile.py to support secondary threads. r=vlad

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extra : rebase_source : 28357bbb17b15c7cb40c53ee3442bc6366fcf015