Rewire Android WebView's compositor changed signal.

android_webview/browser/compositor_id.cc

+// 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.
+
+#include "android_webview/browser/compositor_id.h"
+#include "content/public/common/child_process_host.h"
+
+namespace android_webview {
+
+CompositorID::CompositorID()
+    : process_id(content::ChildProcessHost::kInvalidUniqueID),
+      routing_id(content::ChildProcessHost::kInvalidUniqueID) {}

[boliu, 2016/06/13 15:30:44]

does this apply to routing_id too?

either way, I think it should be possible to get rid of this constructor
altogether?

[hush (inactive), 2016/06/14 23:48:28]

it does apply to routing_id. Example here:
https://cs.chromium.org/chromium/src/chrome/browser/printing/printing_message...

The reason I need this constructor is that I need them to be default initialized
to an invalid value.

+
+CompositorID::CompositorID(int process_id, int routing_id)
+    : process_id(process_id), routing_id(routing_id) {}
+
+CompositorID::CompositorID(const CompositorID& other) = default;
+
+CompositorID& CompositorID::operator=(const CompositorID& other) {
+  process_id = other.process_id;
+  routing_id = other.routing_id;
+  return *this;
+}
+
+bool operator==(const CompositorID& lhs, const CompositorID& rhs) {
+  return lhs.process_id == rhs.process_id && lhs.routing_id == rhs.routing_id;
+}
+
+bool operator<(const CompositorID& lhs, const CompositorID& rhs) {
+  if (lhs.process_id == rhs.process_id) {
+    return lhs.routing_id < rhs.routing_id;
+  }
+  return lhs.process_id < rhs.process_id;
+}
+
+bool operator!=(const CompositorID& lhs, const CompositorID& rhs) {
+  return !(lhs == rhs);
+}
+
+bool operator>(const CompositorID& lhs, const CompositorID& rhs) {
+  return rhs < lhs;
+}
+
+bool operator<=(const CompositorID& lhs, const CompositorID& rhs) {
+  return !(rhs > lhs);
+}
+
+bool operator>=(const CompositorID& lhs, const CompositorID& rhs) {
+  return !(lhs < rhs);
+}
+
+}  // namespace android_webview