Factor out RenderWidgetHostConnector

content/browser/android/render_widget_host_connector.h

Index: content/browser/android/render_widget_host_connector.h
diff --git a/content/browser/android/render_widget_host_connector.h b/content/browser/android/render_widget_host_connector.h
new file mode 100644
index 0000000000000000000000000000000000000000..69c23c5a1bd55d356c9901225e3d8be589eb9e79
--- /dev/null
+++ b/content/browser/android/render_widget_host_connector.h
@@ -0,0 +1,78 @@
+// 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.
+
+#ifndef CONTENT_BROWSER_ANDROID_RENDER_WIDGET_HOST_CONNECTOR_H_
+#define CONTENT_BROWSER_ANDROID_RENDER_WIDGET_HOST_CONNECTOR_H_
+
+#include "base/memory/weak_ptr.h"
+#include "content/browser/renderer_host/render_widget_host_view_android.h"
+#include "content/public/browser/web_contents_observer.h"
+
+namespace content {
+
+// An base class used to connect an object of the content layer lifecycle
+// to |RenderWidgetHostViewAndroid|. The inherting class needs to
+// override |UpdateRenderProcessConnection| to set itself to the RWHVA
+// brought up foreground, and null out its reference in the RWHVA going
+// away so it won't access the object any more.

[boliu, 2017/04/13 21:26:59]

definitely should mention this object "owns itself", and is deleted when
WebContents is deleted

[Jinsuk Kim, 2017/04/13 23:00:43]

Done.

+class RenderWidgetHostConnector {
+ public:
+  explicit RenderWidgetHostConnector(WebContents* web_contents);
+  virtual ~RenderWidgetHostConnector();
+
+  // Method to set itself to the |new_rwhva|, and null out the reference
+  // in |old_rwvha|. Example:
+  //
+  // if (old_rwhva)
+  //   old_rwhva->set_object(nullptr);
+  // if (new_rwhva)
+  //   new_rwhva->set_object(this);
+  virtual void UpdateRenderProcessConnection(
+      RenderWidgetHostViewAndroid* old_rwhva,
+      RenderWidgetHostViewAndroid* new_rhwva) = 0;
+
+  RenderWidgetHostViewAndroid* rwhva_for_testing() const {
+    return render_widget_observer_->rwhva();
+  }
+
+ private:
+  // Observes RenderWidgetHostViewAndroid to keep the instance up to date.
+  class Observer : public WebContentsObserver,
+                   public RenderWidgetHostViewAndroid::DestructionObserver {
+   public:
+    Observer(WebContents* web_contents, RenderWidgetHostConnector* connector);
+    ~Observer() override;
+
+    // WebContentsObserver implementation.
+    void RenderViewHostChanged(RenderViewHost* old_host,
+                               RenderViewHost* new_host) override;
+    void DidAttachInterstitialPage() override;
+    void DidDetachInterstitialPage() override;
+    void WebContentsDestroyed() override;
+
+    // RenderWidgetHostViewAndroid::DestructionObserver implementation.
+    void RenderWidgetHostViewDestroyed(
+        RenderWidgetHostViewAndroid* rwhva) override;
+
+    RenderWidgetHostViewAndroid* rwhva() const { return rwhva_; }
+
+   private:
+    void UpdateRenderWidgetHostView(RenderWidgetHostViewAndroid* old_rwhva,
+                                    RenderWidgetHostViewAndroid* new_rwhva);
+    RenderWidgetHostViewAndroid* GetRenderWidgetHostViewAndroid() const;
+
+    RenderWidgetHostConnector* const connector_;
+    RenderWidgetHostViewAndroid* rwhva_;
+
+    DISALLOW_COPY_AND_ASSIGN(Observer);
+  };
+
+  std::unique_ptr<Observer> render_widget_observer_;

[boliu, 2017/04/13 21:26:59]

oh this is unique_ptr now, then you can move the entire Observer declaration
into .cc file, and just leave a forward declaration here

[Jinsuk Kim, 2017/04/13 23:00:43]

Connector::rwhva_for_testing() uses Observer::rwhva() at line 35 for which the
header declaration is necessary here. It's not used now but will be when I put
back the tests. Or do you want the method to be defined in .cc too?

[boliu, 2017/04/13 23:03:32]

Yes. rwhva_for_testing shouldn't be inlined anyway, so should be renamed
GetRenderWidgetHostViewAndroidForTesting

[Jinsuk Kim, 2017/04/13 23:31:10]

Done. Renamed the class to be more descriptive as it's not an inner class any
more.

[boliu, 2017/04/13 23:33:38]

Hmm? It can stay an private inner class. You can forward declare inner classes
too
private:
  class Observer;
  unique_ptr<Observer> observer_;

[Jinsuk Kim, 2017/04/13 23:45:14]

Haven't done that before... Thanks. Done.

+
+  DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostConnector);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ANDROID_RENDER_WIDGET_HOST_CONNECTOR_H_