Android: changed name of threads created in AsyncTask

This is to give better visibility of the threads which are Chrome's and
threads which are Android's.

Bug: 843745
Change-Id: Ie7f75cb915e70b13ef8957f7320d93d890f23a18
Reviewed-on: https://chromium-review.googlesource.com/1158398Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579828}

third_party/android_async_task/java/src/org/chromium/base/AsyncTask.java

@@ -204,7 +204,7 @@ public abstract class AsyncTask<Params, Progress, Result> {
 
         @Override
         public Thread newThread(Runnable r) {
-            return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
+            return new Thread(r, "CrAsyncTask #" + mCount.getAndIncrement());
         }
     };