Add setting to isolate zoom changes by default.

content/browser/host_zoom_map_impl.h

Index: content/browser/host_zoom_map_impl.h
diff --git a/content/browser/host_zoom_map_impl.h b/content/browser/host_zoom_map_impl.h
index ad4c07e16c4247885814cbccfe96454f79fcfd05..d545016866b730c1ec7b99322cf23c6eb752de65 100644
--- a/content/browser/host_zoom_map_impl.h
+++ b/content/browser/host_zoom_map_impl.h
@@ -36,6 +36,9 @@ class CONTENT_EXPORT HostZoomMapImpl : public NON_EXPORTED_BASE(HostZoomMap),
   void ClearPageScaleFactorIsOneForView(
       int render_process_id, int render_view_id) override;
   void CopyFrom(HostZoomMap* copy) override;
+  void PreserveTemporaryZoomLevelFrom(
+      const HostZoomMap* copy, RenderFrameHost* old_host,
+      RenderFrameHost* new_host) override;
   double GetZoomLevelForHostAndScheme(const std::string& scheme,
                                       const std::string& host) const override;
   // TODO(wjmaclean) Should we use a GURL here? crbug.com/384486
@@ -81,8 +84,8 @@ class CONTENT_EXPORT HostZoomMapImpl : public NON_EXPORTED_BASE(HostZoomMap),
                            const std::string& host);
 
   // Returns the temporary zoom level that's only valid for the lifetime of
-  // the given WebContents (i.e. isn't saved and doesn't affect other
-  // WebContentses) if it exists, the default zoom level otherwise.
+  // 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.
   double GetTemporaryZoomLevel(int render_process_id,