alternate ntp: fix crash in ContentsContainer destructor

chrome/browser/ui/views/frame/contents_container.cc

 // Copyright 2012 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 "chrome/browser/ui/views/frame/contents_container.h"
 
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents.h"
@@ skipping 80 matching lines @@
 
 ContentsContainer::~ContentsContainer() {
 }
 
 void ContentsContainer::MakeOverlayContentsActiveContents() {
   DCHECK(overlay_);
 
   active_ = overlay_;
   overlay_ = NULL;
   overlay_web_contents_ = NULL;
+  // Unregister from observing previous |overlay_web_contents_|.
+  registrar_.RemoveAll();
   // Since |overlay_| has been nuked, shadow view is not needed anymore.
   // Note that the previous |active_| will be deleted by caller (see
   // BrowserView::ActiveTabChanged()) after this call, hence removing the old
   // |active_| as a child, and making the new |active_| (which is the previous
   // |overlay_|) the first child.
   shadow_view_.reset();
   Layout();
 }
 
 void ContentsContainer::SetOverlay(views::WebView* overlay,
@@ skipping 27 matching lines @@
         RemoveChildView(shadow_view_.get());
       RemoveChildView(overlay_);
     }
     overlay_ = overlay;
     if (overlay_)
       AddChildView(overlay_);
   }
 
   if (overlay_web_contents_ != overlay_web_contents) {
 #if !defined(OS_WIN)
-    // Unregister from previous overlay web contents' render view host.
-    if (overlay_web_contents_)
-      registrar_.RemoveAll();
+    // Unregister from observing previous |overlay_web_contents_|.
+    registrar_.RemoveAll();
 #endif  // !defined(OS_WIN)
 
     overlay_web_contents_ = overlay_web_contents;
 
 #if !defined(OS_WIN)
     // Register to new overlay web contents' render view host.
     if (overlay_web_contents_) {
       content::RenderViewHost* rvh = overlay_web_contents_->GetRenderViewHost();
       DCHECK(rvh);
-      content::NotificationSource source =
-          content::Source<content::RenderWidgetHost>(rvh);
-      registrar_.Add(this,
-          content::NOTIFICATION_RENDER_WIDGET_HOST_DID_UPDATE_BACKING_STORE,
-          source);
+      if (rvh) {
+        content::NotificationSource source =
+            content::Source<content::RenderWidgetHost>(rvh);
+        registrar_.Add(this,
+            content::NOTIFICATION_RENDER_WIDGET_HOST_DID_UPDATE_BACKING_STORE,
+            source);
+      }
     }
 #endif  // !defined(OS_WIN)
   }
 
   overlay_height_ = height;
   overlay_height_units_ = units;
   draw_drop_shadow_ = draw_drop_shadow;
 
   // Add shadow view if there's overlay and drop shadow is needed.
   // Remove shadow view if there's no overlay.
@@ skipping 91 matching lines @@
 std::string ContentsContainer::GetClassName() const {
   return kViewClassName;
 }
 
 void ContentsContainer::Observe(int type,
                                 const content::NotificationSource& source,
                                 const content::NotificationDetails& details) {
   DCHECK_EQ(content::NOTIFICATION_RENDER_WIDGET_HOST_DID_UPDATE_BACKING_STORE,
             type);
   // Remove shadow view if it's not needed.
-  if (overlay_ && !draw_drop_shadow_)
+  if (overlay_ && !draw_drop_shadow_) {
+    DCHECK(overlay_web_contents_);
+    DCHECK_EQ(overlay_web_contents_->GetRenderViewHost(),
+              (content::Source<content::RenderWidgetHost>(source)).ptr());
     shadow_view_.reset();
+  }
 }