Add setting to isolate zoom changes by default.

content/public/browser/zoom_level_delegate.h

Index: content/public/browser/zoom_level_delegate.h
diff --git a/content/public/browser/zoom_level_delegate.h b/content/public/browser/zoom_level_delegate.h
index e6a93bde06ef2f09c3b5d8c7b46d329b1be0a22e..370009d7080ecb28637f4ec011a06cbc5942c701 100644
--- a/content/public/browser/zoom_level_delegate.h
+++ b/content/public/browser/zoom_level_delegate.h
@@ -5,14 +5,25 @@
 #ifndef CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_DELEGATE_H_
 #define CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_DELEGATE_H_
 
+#include "base/callback_list.h"
+
 namespace content {
 
 class HostZoomMap;
 
-// An interface to allow the client to initialize the HostZoomMap.
+// An interface to allow the client to initialize the HostZoomMap
+// and to know the default zoom scope.
 class ZoomLevelDelegate {
  public:
+  typedef base::CallbackList<void(void)>::Subscription
+      DefaultZoomScopeSubscription;
+
   virtual void InitHostZoomMap(HostZoomMap* host_zoom_map) = 0;
+
+  virtual bool GetIsOriginScopePref() const = 0;
+  virtual std::unique_ptr<DefaultZoomScopeSubscription>
+  RegisterDefaultZoomScopeCallback(const base::Closure& callback) = 0;
+
   virtual ~ZoomLevelDelegate() {}
 };