Add setting to isolate zoom changes by default.

content/public/browser/host_zoom_map.h

 // Copyright (c) 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_
 #define CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 130 matching lines @@
   // This should only be called on the UI thread.
   virtual void SetZoomLevelForHostAndScheme(const std::string& scheme,
                                             const std::string& host,
                                             double level) = 0;
 
   // Returns whether the view manages its zoom level independently of other
   // views displaying content from the same host.
   virtual bool UsesTemporaryZoomLevel(int render_process_id,
                                       int render_view_id) const = 0;
 
-  // Sets the temporary zoom level that's only valid for the lifetime of this
-  // WebContents.
+  // Returns the temporary zoom level that's only valid for the lifetime of
+  // the given view (i.e. isn't saved and doesn't affect other WebContentses)
+  // if it exists, the default zoom level otherwise.
+  //
+  // This may be called on any thread.
+  virtual double GetTemporaryZoomLevel(int render_process_id,
+                                       int render_view_id) const = 0;
+
+  // Sets the temporary zoom level that's only valid for the lifetime of the
+  // given view.
   //
   // This should only be called on the UI thread.
   virtual void SetTemporaryZoomLevel(int render_process_id,
                                      int render_view_id,
                                      double level) = 0;
 
-  // Clears the temporary zoom level stored for this WebContents.
+  // Clears the temporary zoom level stored for the given view.
   //
   // This should only be called on the UI thread.
   virtual void ClearTemporaryZoomLevel(int render_process_id,
                                        int render_view_id) = 0;
 
   // Get/Set the default zoom level for pages that don't override it.
   virtual double GetDefaultZoomLevel() const = 0;
   virtual void SetDefaultZoomLevel(double level) = 0;
 
   typedef base::Callback<void(const ZoomLevelChange&)> ZoomLevelChangedCallback;
   typedef base::CallbackList<void(const ZoomLevelChange&)>::Subscription
       Subscription;
   // Add and remove zoom level changed callbacks.
   virtual std::unique_ptr<Subscription> AddZoomLevelChangedCallback(
       const ZoomLevelChangedCallback& callback) = 0;
 
  protected:
   virtual ~HostZoomMap() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_