Add setting to isolate zoom changes by default.

content/public/browser/web_contents.h

Index: content/public/browser/web_contents.h
diff --git a/content/public/browser/web_contents.h b/content/public/browser/web_contents.h
index a5e25357162ed23c75c10f613567c16cf8d84e25..5f75dc298c64909abc53c0130f019a1ee322db2f 100644
--- a/content/public/browser/web_contents.h
+++ b/content/public/browser/web_contents.h
@@ -277,6 +277,10 @@ class WebContents : public PageNavigator,
   // handler.
   virtual void ClosePage() = 0;
 
+  // Notifies the WebContents of its replacement by another WebContents
+  // in a browser tab.
+  virtual void OnReplaced(WebContents* new_contents) = 0;

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

Hmm, content/ isn't supposed to know anything about "tabs", so we'll need some
other description for this, or move the concept into chrome/.

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

Done.

Removed.

+
   // Returns the currently active fullscreen widget. If there is none, returns
   // nullptr.
   virtual RenderWidgetHostView* GetFullscreenRenderWidgetHostView() const = 0;