Don't re-use a zoom bubble unless it has the same web-contents.

chrome/browser/ui/views/location_bar/zoom_bubble_view.cc

Index: chrome/browser/ui/views/location_bar/zoom_bubble_view.cc
diff --git a/chrome/browser/ui/views/location_bar/zoom_bubble_view.cc b/chrome/browser/ui/views/location_bar/zoom_bubble_view.cc
index 081b8b2e8256a50a55c2c71cda00e17a0e5a41c7..fd6b6ae60c3610ce61b5e46b7f56b0e313f30f52 100644
--- a/chrome/browser/ui/views/location_bar/zoom_bubble_view.cc
+++ b/chrome/browser/ui/views/location_bar/zoom_bubble_view.cc
@@ -69,6 +69,7 @@ void ZoomBubbleView::ShowBubble(content::WebContents* web_contents,
   if (zoom_bubble_ &&
       zoom_bubble_->GetAnchorView() == anchor_view &&
       !extension) {
+    DCHECK_EQ(web_contents, zoom_bubble_->web_contents_);
     zoom_bubble_->Refresh();
     return;
   }
@@ -174,6 +175,10 @@ void ZoomBubbleView::Refresh() {
 }
 
 void ZoomBubbleView::Close() {
+  // Widget's Close() is async, but we don't want to use zoom_bubble_ after
+  // this. Additionally web_contents_ may have been destroyed.
+  zoom_bubble_ = NULL;
+  web_contents_ = NULL;
   GetWidget()->Close();
 }