Rewire Android WebView's compositor changed signal.

android_webview/browser/compositor_id.h

+// 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.
+
+#ifndef ANDROID_WEBVIEW_BROWSER_COMPOSITOR_ID_H_
+#define ANDROID_WEBVIEW_BROWSER_COMPOSITOR_ID_H_
+
+namespace android_webview {
+
+struct CompositorID {
+  CompositorID();
+  CompositorID(int process_id, int routing_id);
+  CompositorID(const CompositorID& other);
+  CompositorID& operator=(const CompositorID& other);
+  bool Equals(const CompositorID& other) const;
+
+  int process_id;
+  int routing_id;
+};
+
+struct CompositorIDComparator {
+  bool operator()(const CompositorID& a, const CompositorID& b) const;
+};
+
+}  // namespace android_webview
+
+#endif  // ANDROID_WEBVIEW_BROWSER_COMPOSITOR_ID_H_