alternate ntp: fix crash in ContentsContainer destructor

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

Index: chrome/browser/ui/views/frame/contents_container.cc
diff --git a/chrome/browser/ui/views/frame/contents_container.cc b/chrome/browser/ui/views/frame/contents_container.cc
index 4603f9ad3e48af8d39346db592288a6423291ba2..94cd7123be82d4854bdcc1667f06cd7a48a67a00 100644
--- a/chrome/browser/ui/views/frame/contents_container.cc
+++ b/chrome/browser/ui/views/frame/contents_container.cc
@@ -98,6 +98,8 @@ void ContentsContainer::MakeOverlayContentsActiveContents() {
   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
@@ -145,9 +147,8 @@ void ContentsContainer::SetOverlay(views::WebView* 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;
@@ -273,6 +274,9 @@ void ContentsContainer::Observe(int type,
   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_ && overlay_web_contents_ &&
+      (content::Source<content::RenderWidgetHost>(source)).ptr() ==

[sky, 2013/04/05 19:44:17]

Shouldn't this be a DCHECK?

[kuan, 2013/04/05 21:54:11]

this is the dilemma i have:
@159, GetRenderViewHost could return NULL; since my DCHECK is a nop in release
mode, i'll registering for all sources in that case.  i have 2 options:
a) register even if rvh is NULL, then i need to keep the if cond here.
b) only register if rvh is not NULL, then i can change this to DCHECK.

i'm not sure which option is better.

[sky, 2013/04/05 23:00:08]

Only register if rvh is non-null.

[kuan, 2013/04/05 23:10:54]

Done.

+          overlay_web_contents_->GetRenderViewHost()) {
     shadow_view_.reset();
+  }
 }