Factor out RenderWidgetHostConnector

content/browser/android/render_widget_host_connector.h

+// 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/public/browser/web_contents_observer.h"
+
+namespace content {
+
+class RenderWidgetHostViewAndroid;
+
+// An base class used to connect an object of the content layer lifecycle
+// to |RenderWidgetHostViewAndroid|. Observes RenderWidgetHostViewAndroid
+// updates and helps child classes keep it the up-to-date.
+// 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.
+class RenderWidgetHostConnector : public WebContentsObserver {
+ public:
+  explicit RenderWidgetHostConnector(WebContents* web_contents);
+  ~RenderWidgetHostConnector() override;
+
+  // Method to set itself to the |new_view|, and null out the reference
+  // in |old_view|. Example:
+  //
+  // if (old_rwhva)
+  //   old_rwhva->set_object(nullptr);
+  // if (new_rwhva)
+  //   new_rwhva->set_object(this);
+  virtual void UpdateRenderWidgetHostView(
+      RenderWidgetHostViewAndroid* old_rwhva,
+      RenderWidgetHostViewAndroid* new_rwhva) = 0;

[boliu, 2017/04/12 16:29:22]

as discussed in chat, add a client interface so that Connector is composed in
ImeAdapter?

+
+  // WebContentsObserver implementation.
+  void RenderViewHostChanged(RenderViewHost* old_host,
+                             RenderViewHost* new_host) override;
+  void WebContentsDestroyed() override;
+
+ private:
+  RenderWidgetHostViewAndroid* GetRenderWidgetHostView() const;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostConnector);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ANDROID_RENDER_WIDGET_HOST_CONNECTOR_H_