Rename ScopedTaskEnvironment::ExecutionMode

ScopedTaskEnvironment::ExecutionMode is becoming
ScopedTaskEnvironment::ThreadPoolExecutionMode

This CL was uploaded by git cl split.

R=martis@chromium.org

Bug: 708584
Change-Id: If1c963d91c1867c4d3c8564f83e51b7d5f033e78
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583804
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Michael Martis <martis@chromium.org>
Commit-Queue: Michael Martis <martis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654302}
4 files changed