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|. 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:
+  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() const {

[boliu, 2017/04/10 18:08:43]

I mean this getter is not really needed explicitly, or if it is here, it should
match the last "new_rwhva" in UpdateRenderProcessConnection . The
UpdateRenderProcessConnection API already allows observing rwhva destruction as
well, so we should do that. Probably means RWHVA should explicitly tell this
object it's being destroyed though I guess, instead of implicitly through weak
pointer.

[Jinsuk Kim, 2017/04/11 01:41:58]

Removed rwhva() but let ImeAdapterAndroid keep the reference to RWHVA.
I think we already tried the idea but decided to turn to weak ptr as discussed
here
https://codereview.chromium.org/2752113005/diff2/380001:400001/content/browse...
are you okay with going back or mean something different?

[boliu, 2017/04/11 01:47:04]

Yeah I prefer explicit destroy now.

That was a one off where adding a few checks is ok. This is factoring a class,
so should keep the interface simple and safe if possible

[Jinsuk Kim, 2017/04/11 02:28:09]

Done. Could you let me know if there's a reason weak ptr is not preferred? Was
it introduced to a certain limited use only?

[boliu, 2017/04/11 02:34:24]

It's purely to make this interface simpler. If you use weakptrs, then subclass
has to null check rwhva every single time. If you use explicit destroy, then
could just UpdateRenderProcessConnection to null and subclass would just know.

+    return render_widget_observer_.rwhva();
+  }
+
+ private:
+  // Observes RenderWidgetHostViewAndroid updates and keeps the up-to-date
+  // instance through the interface |WebContentsObserver|.
+  class Observer : public WebContentsObserver {
+   public:
+    Observer(WebContents* web_contents, RenderWidgetHostConnector* connector);
+    ~Observer() override;
+
+    // WebContentsObserver implementation.
+    void RenderViewReady() override;
+    void RenderViewHostChanged(RenderViewHost* old_host,
+                               RenderViewHost* new_host) override;
+    void DidAttachInterstitialPage() override;
+    void DidDetachInterstitialPage() override;
+    void WebContentsDestroyed() override;
+
+    RenderWidgetHostViewAndroid* rwhva() const { return rwhva_.get(); }
+
+   private:
+    void UpdateRenderWidgetHostView(RenderWidgetHostViewAndroid* rwhva);
+    RenderWidgetHostViewAndroid* GetRenderWidgetHostViewAndroid() const;
+
+    RenderWidgetHostConnector* connector_;
+    base::WeakPtr<RenderWidgetHostViewAndroid> rwhva_;
+
+    DISALLOW_COPY_AND_ASSIGN(Observer);
+  };
+
+  const Observer render_widget_observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostConnector);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ANDROID_RENDER_WIDGET_HOST_CONNECTOR_H_