Remove AudioWorkletThread from AudioContextTest.cpp

AudioContextTest.cpp tests the audio latency and is not involved
any AudioWorklet operation. Removing AudioWorkletThread addresses
the data race found in the bug.

Locally confirmed that TSAN with this patch does not crash with
the data race any more.

Bug: 792140
Change-Id: I297533a176c42fb1af5025fdcd77a1cf4e68ee56
Reviewed-on: https://chromium-review.googlesource.com/809825Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521866}

third_party/WebKit/Source/modules/webaudio/AudioContextTest.cpp

@@ -8,7 +8,6 @@
 
 #include "core/dom/Document.h"
 #include "core/testing/DummyPageHolder.h"
-#include "modules/webaudio/AudioWorkletThread.h"
 #include "platform/testing/TestingPlatformSupport.h"
 #include "platform/wtf/PtrUtil.h"
 #include "public/platform/WebAudioDevice.h"
@@ -94,7 +93,6 @@ class AudioContextTest : public ::testing::Test {
   }
 
   void SetUp() override {
-    AudioWorkletThread::CreateSharedBackingThreadForTest();
     dummy_page_holder_ = DummyPageHolder::Create();
   }