Rename ScopedTaskEnvironment::ExecutionMode

ScopedTaskEnvironment::ExecutionMode is becoming
ScopedTaskEnvironment::ThreadPoolExecutionMode

This CL was uploaded by git cl split.

R=olka@chromium.org

Bug: 708584
Change-Id: Ib2ce8cf466767729823ce4f5b53891966be6b456
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583794
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Carlos Caballero <carlscab@google.com>
Cr-Commit-Position: refs/heads/master@{#654044}
2 files changed