Reduce the size of execution_context.h.

It is used in 4,300+ compilation units.
http://crrev.com/590155 increased its pre-processed size by 3.72MB, and
this CL fixes it.

Bug: 242216, 881537, 882997
Change-Id: If723b9d77dbd06fdde184498aa6ed7aa3e5e88e2
Reviewed-on: https://chromium-review.googlesource.com/1218388
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590526}
2 files changed