Revert "Rerouting all Java tasks through TaskRunner API"

This reverts commit 8e470e32.

Reason for revert: Suspected cause of flaky timeout of the following test (see issue 925599):
org.chromium.base.task.SingleThreadTaskRunnerImplTest#testPreNativePostTask

Original change's description:
> Rerouting all Java tasks through TaskRunner API
> 
> Pre-native Java tasks are now having their priority set when started.
> Also switches dynamicmodule's ModuleLoader to use the TaskTrait's
> priority setting instead of manually setting the thread priority.
> 
> Bug: 863457
> Change-Id: Iee601ca1e18e2637f8e930c6d212c8115e682fc3
> Reviewed-on: https://chromium-review.googlesource.com/c/1407374
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
> Reviewed-by: Andrew Grieve <agrieve@chromium.org>
> Reviewed-by: Benoit L <lizeb@chromium.org>
> Commit-Queue: Sam Maier <smaier@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#626095}

TBR=yfriedman@chromium.org,skyostil@chromium.org,agrieve@chromium.org,lizeb@chromium.org,smaier@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 863457
Change-Id: I55487d7e6373a1b1d8d346432e3ac59cdde08e41
Reviewed-on: https://chromium-review.googlesource.com/c/1436657Reviewed-by: Yuta Kitamura <yutak@chromium.org>
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626451}

base/android/java/src/org/chromium/base/task/AsyncTask.java

@@ -5,6 +5,7 @@
 package org.chromium.base.task;
 
 import android.os.Binder;
+import android.os.Process;
 import android.support.annotation.IntDef;
 import android.support.annotation.MainThread;
 import android.support.annotation.WorkerThread;
@@ -33,14 +34,10 @@ import java.util.concurrent.atomic.AtomicBoolean;
 public abstract class AsyncTask<Result> {
     private static final String TAG = "AsyncTask";
 
-    private static TaskTraits sLowPriorityTraits =
-            new TaskTraits().setTaskPriority(TaskPriority.LOWEST).setMayBlock(true);
     /**
      * An {@link Executor} that can be used to execute tasks in parallel.
-     * We use the lowest task priority, and mayBlock = true since any user of this could block.
      */
-    public static final Executor THREAD_POOL_EXECUTOR =
-            (Runnable r) -> PostTask.postTask(sLowPriorityTraits, r);
+    public static final Executor THREAD_POOL_EXECUTOR = new ChromeThreadPoolExecutor();
 
     /**
      * An {@link Executor} that executes tasks one at a time in serial
@@ -103,6 +100,7 @@ public abstract class AsyncTask<Result> {
                 mTaskInvoked.set(true);
                 Result result = null;
                 try {
+                    Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
                     result = doInBackground();
                     Binder.flushPendingCommands();
                 } catch (Throwable tr) {
@@ -355,20 +353,6 @@ public abstract class AsyncTask<Result> {
         return this;
     }
 
-    /**
-     * Executes an AsyncTask with the given task traits. Provides no guarantees about sequencing or
-     * which thread it runs on.
-     *
-     * @param taskTraits traits which describe this AsyncTask.
-     * @return This instance of AsyncTask.
-     */
-    @MainThread
-    public final AsyncTask<Result> executeWithTaskTraits(TaskTraits taskTraits) {
-        executionPreamble();
-        PostTask.postTask(taskTraits, mFuture);
-        return this;
-    }
-
     private void finish(Result result) {
         if (isCancelled()) {
             onCancelled(result);

base/android/java/src/org/chromium/base/task/ChromeThreadPoolExecutor.java

@@ -6,8 +6,6 @@ package org.chromium.base.task;
 
 import static java.util.concurrent.TimeUnit.SECONDS;
 
-import android.os.Process;
-
 import org.chromium.base.BuildConfig;
 import org.chromium.base.VisibleForTesting;
 
@@ -36,11 +34,7 @@ class ChromeThreadPoolExecutor extends ThreadPoolExecutor {
         private final AtomicInteger mCount = new AtomicInteger(1);
         @Override
         public Thread newThread(Runnable r) {
-            Thread t = new Thread(() -> {
-                Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
-                r.run();
-            }, "CrAsyncTask #" + mCount.getAndIncrement());
-            return t;
+            return new Thread(r, "CrAsyncTask #" + mCount.getAndIncrement());
         }
     };
 
@@ -115,9 +109,9 @@ class ChromeThreadPoolExecutor extends ThreadPoolExecutor {
     }
 
     @Override
-    public void execute(Runnable r) {
+    public void execute(Runnable command) {
         try {
-            super.execute(r);
+            super.execute(command);
         } catch (RejectedExecutionException e) {
             Map<String, Integer> counts = getNumberOfClassNameOccurrencesInQueue();
 

base/android/java/src/org/chromium/base/task/TaskRunnerImpl.java

@@ -4,7 +4,6 @@
 
 package org.chromium.base.task;
 
-import android.os.Process;
 import android.support.annotation.Nullable;
 import android.util.Pair;
 
@@ -22,6 +21,7 @@ import java.util.List;
  */
 @JNINamespace("base")
 public class TaskRunnerImpl implements TaskRunner {
+    @Nullable
     private final TaskTraits mTaskTraits;
     private final String mTraceEvent;
     private final @TaskRunnerType int mTaskRunnerType;
@@ -30,8 +30,6 @@ public class TaskRunnerImpl implements TaskRunner {
     protected final Runnable mRunPreNativeTaskClosure = this::runPreNativeTask;
     private boolean mIsDestroying;
     private final GcStateAssert mGcStateAssert = GcStateAssert.create(this, true);
-    private static final ChromeThreadPoolExecutor THREAD_POOL_EXECUTOR =
-            new ChromeThreadPoolExecutor();
 
     @Nullable
     protected LinkedList<Runnable> mPreNativeTasks = new LinkedList<>();
@@ -101,7 +99,7 @@ public class TaskRunnerImpl implements TaskRunner {
      * time.
      */
     protected void schedulePreNativeTask() {
-        THREAD_POOL_EXECUTOR.execute(mRunPreNativeTaskClosure);
+        AsyncTask.THREAD_POOL_EXECUTOR.execute(mRunPreNativeTaskClosure);
     }
 
     /**
@@ -114,18 +112,6 @@ public class TaskRunnerImpl implements TaskRunner {
                 if (mPreNativeTasks == null) return;
                 task = mPreNativeTasks.poll();
             }
-
-            switch (mTaskTraits.mPriority) {
-                case TaskPriority.USER_VISIBLE:
-                    Process.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
-                    break;
-                case TaskPriority.HIGHEST:
-                    Process.setThreadPriority(Process.THREAD_PRIORITY_MORE_FAVORABLE);
-                    break;
-                default:
-                    Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
-                    break;
-            }
             task.run();
         }
     }

chrome/android/java/src/org/chromium/chrome/browser/customtabs/dynamicmodule/ModuleLoader.java

@@ -12,6 +12,7 @@ import android.content.pm.PackageInfo;
 import android.content.pm.PackageManager;
 import android.os.Bundle;
 import android.os.IBinder;
+import android.os.Process;
 import android.support.annotation.Nullable;
 
 import dalvik.system.DexClassLoader;
@@ -23,8 +24,6 @@ import org.chromium.base.Log;
 import org.chromium.base.ObserverList;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.task.AsyncTask;
-import org.chromium.base.task.TaskPriority;
-import org.chromium.base.task.TaskTraits;
 import org.chromium.chrome.browser.ChromeApplication;
 import org.chromium.chrome.browser.ChromeFeatureList;
 import org.chromium.chrome.browser.customtabs.dynamicmodule.ModuleMetrics.DestructionReason;
@@ -155,10 +154,7 @@ public class ModuleLoader {
         ModuleMetrics.registerLifecycleState(ModuleMetrics.LifecycleState.NOT_LOADED);
 
         mIsModuleLoading = true;
-        new LoadClassTask(moduleContext)
-                .executeWithTaskTraits(new TaskTraits()
-                                               .setTaskPriority(TaskPriority.USER_VISIBLE)
-                                               .setMayBlock(true));
+        new LoadClassTask(moduleContext).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }
 
     /**
@@ -330,7 +326,16 @@ public class ModuleLoader {
         @Override
         @Nullable
         protected Class<?> doInBackground() {
+            int oldPriority = Process.getThreadPriority(0);
             try {
+                // We don't want to block the UI thread, but we don't want to be really slow either.
+                // The AsyncTask class sets the thread priority quite low
+                // (THREAD_PRIORITY_BACKGROUND) and does not distinguish between user-visible
+                // user-invisible tasks.
+                // TODO(crbug.com/863457): Replace this with something like a task trait that
+                // influences priority once we have a task scheduler in Java.
+                Process.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT);
+
                 boolean loadFromDex = updateModuleDexInDiskIfNeeded();
                 long entryPointLoadClassStartTime = ModuleMetrics.now();
                 Class<?> clazz =
@@ -344,6 +349,8 @@ public class ModuleLoader {
                 Log.e(TAG, "Could not copy dex to local storage", e);
                 ModuleMetrics.recordLoadResult(
                         ModuleMetrics.LoadResult.FAILED_TO_COPY_DEX_EXCEPTION);
+            } finally {
+                Process.setThreadPriority(oldPriority);
             }
             return null;
         }