TtsPlatformImpl: Use async trace event for async computation

The "TtsPlatformImpl:initialize" event is used around an async task
that executes in the background, thus should be an async trace event
outside the current thread's track.

Change-Id: Icc89048a1c7e2a9659e12fbe74d5b0600b6becf1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2252166
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Auto-Submit: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780336}

content/public/android/java/src/org/chromium/content/browser/TtsPlatformImpl.java

@@ -279,7 +279,7 @@ class TtsPlatformImpl implements ActivityStateListener {
      * we can call TtsPlatformImplJni.get().voicesChanged directly.
      */
     private void initialize() {
-        TraceEvent.begin("TtsPlatformImpl:initialize");
+        TraceEvent.startAsync("TtsPlatformImpl:initialize", hashCode());
 
         new AsyncTask<List<TtsVoice>>() {
             @Override
@@ -323,7 +323,8 @@ class TtsPlatformImpl implements ActivityStateListener {
 
                 if (mPendingUtterance != null) mPendingUtterance.speak();
 
-                TraceEvent.end("TtsPlatformImpl:initialize");
+                TraceEvent.finishAsync(
+                        "TtsPlatformImpl:initialize", TtsPlatformImpl.this.hashCode());
             }
         }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }