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This integrates the recently added TaskAnnotator IPC message
decoration into Mojo and legacy IPC handlers. This causes all
PendingTask objects to be decorated with a program counter that
uniquely identifies the IPC message that was being handled when
that task was posted.

This work is discussed in the following design doc:

https://docs.google.com/document/d/1soCnDaQUug_Q4oadX1YxynjzookCh9Aj1fL-HOCwnEY/edit?pli=1#

The net binary size impact is O(50kB) across platforms, which after
much discussion was deemed a reasonable trade off.

BUG=950668

Change-Id: Ibf36cf177b09f8ed8919fd19caebce137249c4c6
Binary-Size: Increase due to new instrumentation.
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1586318
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#654837}