AndroidOverlay implementation using Dialog.

content/public/android/java/src/org/chromium/content/browser/androidoverlay/ThreadHoppingHost.java

+// Copyright 2017 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.content.browser.androidoverlay;
+
+import android.os.Handler;
+import android.view.Surface;
+
+import java.util.concurrent.Semaphore;
+
+/**
+ * DialogOverlayCore::Host implementation that transfers messages to the thread on which it was
+ * constructed.  Due to threading concerns, waitForCleanup is not forwarded.
+ */
+class ThreadHoppingHost implements DialogOverlayCore.Host {
+    // Handler for the host we're proxying to.  Typically Browser::UI.
+    private Handler mHandler;
+
+    // Host impl that we're proxying to.
+    private final DialogOverlayCore.Host mHost;
+
+    // Semaphore to keep track of whether cleanup has started yet.
+    private final Semaphore mSemaphore = new Semaphore(0);
+
+    // We will forward to |host| on whatever thread we're constructed on.
+    public ThreadHoppingHost(DialogOverlayCore.Host host) {
+        mHandler = new Handler();
+        mHost = host;
+    }
+
+    @Override
+    public void onSurfaceReady(final Surface surface) {
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                mHost.onSurfaceReady(surface);
+            }
+        });
+    }
+
+    @Override
+    public void onOverlayDestroyed() {
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                mHost.onOverlayDestroyed();
+            }
+        });
+    }
+
+    // We don't forward via to |mHandler|, since it should be asynchronous.  Else, the |mHandler|
+    // thread would block.  Instead, we wait here and somebody must call onCleanup() to let us know
+    // that cleanup has started, and that we may return.
+    @Override
+    public void waitForCleanup() {
+        while (true) {
+            try {
+                mSemaphore.acquire();
+                break;
+            } catch (InterruptedException e) {
+            }
+        }
+    }
+
+    // Notify us that cleanup has started.  This is called on |mHandler|'s thread.
+    public void onCleanup() {
+        mSemaphore.release(1);
+    }
+}