base: Add scope support to context trace events

Make it possible to use context ids that are specific to a scope.

BUG=546021

Review URL: https://codereview.chromium.org/1645853003

Cr-Original-Commit-Position: refs/heads/master@{#372967}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 8f01592f0b53ed7a1a509faf6730e9b699a27abc
1 file changed
tree: 7ceef6595952dbabc905deeb3f6ec6268f1630e6
  1. trace_event_common.h