Add setting to isolate zoom changes by default.

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index 74218f22e802ac54244c7f3ca99d489e54964093..b1a219c7964ec00e4c3c7a0085ee5c959a53db78 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -406,6 +406,10 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   virtual void DidCloneToNewWebContents(WebContents* old_web_contents,
                                         WebContents* new_web_contents) {}
 
+  // Invoked when a tab's WebContents is replaced with another.

[wjmaclean, 2017/01/19 21:09:06]

Ditto.

[Kevin McNee, 2017/01/25 23:42:56]

Done.

Removed.

+  virtual void WebContentsReplaced(WebContents* old_web_contents,
+                                   WebContents* new_web_contents) {}
+
   // Invoked when the WebContents is being destroyed. Gives subclasses a chance
   // to cleanup. After the whole loop over all WebContentsObservers has been
   // finished, web_contents() returns nullptr.