Add setting to isolate zoom changes by default.

components/zoom/zoom_prefs_delegate.h

Index: components/zoom/zoom_prefs_delegate.h
diff --git a/components/zoom/zoom_prefs_delegate.h b/components/zoom/zoom_prefs_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..a27e8ddacb9835cf1d0a7cf5cb46b50d0d43facc
--- /dev/null
+++ b/components/zoom/zoom_prefs_delegate.h
@@ -0,0 +1,28 @@
+// Copyright (c) 2017 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 COMPONENTS_ZOOM_ZOOM_PREFS_DELEGATE_H_
+#define COMPONENTS_ZOOM_ZOOM_PREFS_DELEGATE_H_
+
+#include "base/callback_list.h"
+#include "content/public/browser/zoom_level_delegate.h"
+
+namespace zoom {
+
+// An interface to allow ZoomController to know the default zoom scope pref.
+class ZoomPrefsDelegate : public content::ZoomLevelDelegate {
+ public:
+  typedef base::CallbackList<void(void)>::Subscription
+      DefaultZoomScopeSubscription;
+
+  virtual bool GetZoomScopeIsPerOriginPref() const = 0;
+  virtual std::unique_ptr<DefaultZoomScopeSubscription>
+  RegisterDefaultZoomScopeCallback(const base::Closure& callback) = 0;
+
+  static constexpr bool kZoomScopeSettingDefault = true;
+};
+
+}  // namespace zoom
+
+#endif  // COMPONENTS_ZOOM_ZOOM_PREFS_DELEGATE_H_