Revert "Android: removing default execute() on AsyncTask"

This reverts commit be62a5ba.

Reason for revert: Causes compile failure on many bots:

 ../../components/cronet/android/test/javaperftests/src/org/chromium/net/CronetPerfTestActivity.java:625: error: cannot find symbol
        new BenchmarkTask().execute();

https://ci.chromium.org/buildbot/chromium.android/Android%20Cronet%20Marshmallow%2064bit%20Perf/24049

Original change's description:
> Android: removing default execute() on AsyncTask
> 
> execute() is a confusing function, with a hidden implicit meaning that
> changed in API 11. It would be better if everyone had to use the more
> explicit executeOnExecutor() so their preference (serial or thread pool)
> is called out.
> 
> Bug: 869907
> Change-Id: I79be6d2b3114cb0520df1104ec5849f7c070c99e
> Reviewed-on: https://chromium-review.googlesource.com/1172446
> Reviewed-by: agrieve <agrieve@chromium.org>
> Commit-Queue: Sam Maier <smaier@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#584189}

TBR=agrieve@chromium.org,smaier@chromium.org

Change-Id: I9184afddb3028649c88f9fdf80ea46c4f7cc7806
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 869907
Reviewed-on: https://chromium-review.googlesource.com/1179352Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584211}

base/test/android/junit/src/org/chromium/base/test/asynctask/BackgroundShadowAsyncTask.java

@@ -29,13 +29,13 @@ public class BackgroundShadowAsyncTask<Result> extends ShadowAsyncTask<Result> {
 
     @Override
     @Implementation
-    public final AsyncTask<Result> executeOnExecutor(Executor e) {
+    public final AsyncTask<Result> execute() {
         try {
             return sExecutorService
                     .submit(new Callable<AsyncTask<Result>>() {
                         @Override
                         public AsyncTask<Result> call() throws Exception {
-                            return BackgroundShadowAsyncTask.super.executeInRobolectric();
+                            return BackgroundShadowAsyncTask.super.execute();
                         }
                     })
                     .get();
@@ -45,6 +45,12 @@ public class BackgroundShadowAsyncTask<Result> extends ShadowAsyncTask<Result> {
         }
     }
 
+    @Override
+    @Implementation
+    public final AsyncTask<Result> executeOnExecutor(Executor e) {
+        return execute();
+    }
+
     @Override
     @Implementation
     public final Result get() {

base/test/android/junit/src/org/chromium/base/test/asynctask/CustomShadowAsyncTask.java

@@ -22,6 +22,6 @@ public class CustomShadowAsyncTask<Result> extends ShadowAsyncTask<Result> {
     @Override
     @Implementation
     public final AsyncTask<Result> executeOnExecutor(Executor executor) {
-        return super.executeInRobolectric();
+        return super.execute();
     }
 }

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

@@ -143,7 +143,7 @@ import java.util.concurrent.atomic.AtomicInteger;
  *     <li>The AsyncTask class must be loaded on the UI thread. This is done
  *     automatically as of {@link android.os.Build.VERSION_CODES#JELLY_BEAN}.</li>
  *     <li>The task instance must be created on the UI thread.</li>
- *     <li>{@link #executeOnExecutor(Executor)} must be invoked on the UI thread.</li>
+ *     <li>{@link #execute} must be invoked on the UI thread.</li>
  *     <li>Do not call {@link #onPreExecute()}, {@link #onPostExecute},
  *     {@link #doInBackground} manually.</li>
  *     <li>The task can be executed only once (an exception will be thrown if
@@ -207,6 +207,8 @@ public abstract class AsyncTask<Result> {
     private static final int MESSAGE_POST_RESULT = 0x1;
     private static final int MESSAGE_POST_PROGRESS = 0x2;
 
+    private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
+
     private static final StealRunnableHandler STEAL_RUNNABLE_HANDLER = new StealRunnableHandler();
 
     private final Callable<Result> mWorker;
@@ -407,7 +409,9 @@ public abstract class AsyncTask<Result> {
     }
 
     /**
-     * Override this method to perform a computation on a background thread.
+     * Override this method to perform a computation on a background thread. The
+     * specified parameters are the parameters passed to {@link #execute}
+     * by the caller of this task.
      *
      * @return A result, defined by the subclass of this task.
      *
@@ -560,6 +564,37 @@ public abstract class AsyncTask<Result> {
         return mFuture.get(timeout, unit);
     }
 
+    /**
+     * Executes the task with the specified parameters. The task returns
+     * itself (this) so that the caller can keep a reference to it.
+     *
+     * <p>Note: this function schedules the task on a queue for a single background
+     * thread or pool of threads depending on the platform version.  When first
+     * introduced, AsyncTasks were executed serially on a single background thread.
+     * Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
+     * to a pool of threads allowing multiple tasks to operate in parallel. Starting
+     * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are back to being
+     * executed on a single thread to avoid common application errors caused
+     * by parallel execution.  If you truly want parallel execution, you can use
+     * the {@link #executeOnExecutor} version of this method
+     * with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings
+     * on its use.
+     *
+     * <p>This method must be invoked on the UI thread.
+     *
+     * @return This instance of AsyncTask.
+     *
+     * @throws IllegalStateException If {@link #getStatus()} returns either
+     *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
+     *
+     * @see #executeOnExecutor(java.util.concurrent.Executor)
+     * @see #execute(Runnable)
+     */
+    @MainThread
+    public final AsyncTask<Result> execute() {
+        return executeOnExecutor(sDefaultExecutor);
+    }
+
     /**
      * Executes the task with the specified parameters. The task returns
      * itself (this) so that the caller can keep a reference to it.
@@ -589,6 +624,8 @@ public abstract class AsyncTask<Result> {
      *
      * @throws IllegalStateException If {@link #getStatus()} returns either
      *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
+     *
+     * @see #execute()
      */
     @SuppressWarnings({"MissingCasesInEnumSwitch"})
     @MainThread
@@ -614,6 +651,19 @@ public abstract class AsyncTask<Result> {
         return this;
     }
 
+    /**
+     * Convenience version of {@link #execute()} for use with
+     * a simple Runnable object. See {@link #execute()} for more
+     * information on the order of execution.
+     *
+     * @see #execute()
+     * @see #executeOnExecutor(java.util.concurrent.Executor)
+     */
+    @MainThread
+    public static void execute(Runnable runnable) {
+        sDefaultExecutor.execute(runnable);
+    }
+
     private void finish(Result result) {
         if (isCancelled()) {
             onCancelled(result);

third_party/robolectric/custom_asynctask/java/src/org/chromium/base/test/asynctask/ShadowAsyncTask.java

@@ -88,7 +88,9 @@ public class ShadowAsyncTask<Result> {
         return future.get(timeout, unit);
     }
 
-    public AsyncTask<Result> executeInRobolectric() {
+    @SuppressWarnings("unchecked")
+    @Implementation
+    public AsyncTask<Result> execute() {
         status = AsyncTask.Status.RUNNING;
         getBridge().onPreExecute();