Rename ScopedTaskEnvironment::ExecutionMode

ScopedTaskEnvironment::ExecutionMode is becoming
ScopedTaskEnvironment::ThreadPoolExecutionMode

This CL was uploaded by git cl split.

R=yuweih@chromium.org

Bug: 708584
Change-Id: Ib721ce0db3f4897daf8208c15c2eff99d042360a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583790
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Yuwei Huang <yuweih@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654149}
4 files changed