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1. Adds browser tests for heap profiling with pseudo and no stack mode.
2. TraceLog does not dcheck if filters are added multiple times.
Reason: The EnableHeapProfiling() mojo message from browser to renderer
is sent before OnBeginTracing IPC message. The tracing is being
converted to service and maybe we will have better fix in future.
3. Whitelist heap profiling overhead dumps for background mode.

BUG=700245

Change-Id: I73289e4f7ec5de1421ac44e87e7c30d363869b5b
Reviewed-on: https://chromium-review.googlesource.com/653782
Commit-Queue: Siddhartha S <ssid@chromium.org>
Reviewed-by: Primiano Tucci <primiano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501439}