Rename ScopedTaskEnvironment::ExecutionMode

ScopedTaskEnvironment::ExecutionMode is becoming
ScopedTaskEnvironment::ThreadPoolExecutionMode

This CL was uploaded by git cl split.

R=wutao@chromium.org

Bug: 708584
Change-Id: I5f470dd7236cc340ecc20c6b971843c8e64a5de5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583887
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Tao Wu <wutao@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654786}

chromeos/services/assistant/platform/audio_output_provider_impl_unittest.cc

@@ -81,7 +81,8 @@ class AudioDeviceOwnerTest : public testing::Test {
  public:
   AudioDeviceOwnerTest()
       : task_env_(base::test::ScopedTaskEnvironment::MainThreadType::DEFAULT,
-                  base::test::ScopedTaskEnvironment::ExecutionMode::QUEUED) {}
+                  base::test::ScopedTaskEnvironment::ThreadPoolExecutionMode::
+                      QUEUED) {}
 
   ~AudioDeviceOwnerTest() override { task_env_.RunUntilIdle(); }