Add a general purpose facility for letting background tasks wait until

chrome/android/java/src/org/chromium/chrome/browser/ChromeBackgroundServiceWaiter.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeBackgroundServiceWaiter.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeBackgroundServiceWaiter.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeBackgroundServiceWaiter.java
new file mode 100644
index 0000000000000000000000000000000000000000..5e1544f45e7abfdb65a09e1a3a551aad0db0c935
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeBackgroundServiceWaiter.java
@@ -0,0 +1,50 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser;
+
+import org.chromium.base.Log;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Class to wait for a task to complete before releasing control back to the caller.
+ */
+public class ChromeBackgroundServiceWaiter {
+    private static final String TAG = "CBSWaiter";
+    /** Synchronization object to control the wait. */
+    private final CountDownLatch mLatch;
+    /** How long to wait for before giving up */
+    private int mWakelockTimeoutSeconds;
+
+    public ChromeBackgroundServiceWaiter(int wakelockTimeoutSeconds) {
+        mWakelockTimeoutSeconds = wakelockTimeoutSeconds;
+        mLatch = new CountDownLatch(1);
+    }
+
+    /**
+     * Wait, blocking the current thread until another thread calls onWaitDone.
+     */
+    public void startWaiting() {
+        try {
+            boolean waitSucceeded = mLatch.await(mWakelockTimeoutSeconds, TimeUnit.SECONDS);
+            if (!waitSucceeded) {
+                Log.d(TAG, "waiting for latch timed out");
+            }
+        } catch (InterruptedException e) {
+            Log.d(TAG, "ChromeBackgroundServiceWaiter interrupted while holding wake lock. " + e);
+        }
+    }
+
+
+    /**
+     * Called when the wait is complete.
+     */
+    public void onWaitDone() {
+        // Release the waited thread to return to the caller, and thus release the wake lock held on
+        // behalf of the Owner.
+        mLatch.countDown();
+    }
+}