Add setting to isolate zoom changes by default.

chrome/browser/ui/zoom/chrome_zoom_prefs_helper.h

Index: chrome/browser/ui/zoom/chrome_zoom_prefs_helper.h
diff --git a/chrome/browser/ui/zoom/chrome_zoom_prefs_helper.h b/chrome/browser/ui/zoom/chrome_zoom_prefs_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..1e848c7de480448d667505363b7916e7170c5816
--- /dev/null
+++ b/chrome/browser/ui/zoom/chrome_zoom_prefs_helper.h
@@ -0,0 +1,55 @@
+// Copyright 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 CHROME_BROWSER_UI_ZOOM_CHROME_ZOOM_PREFS_HELPER_H_
+#define CHROME_BROWSER_UI_ZOOM_CHROME_ZOOM_PREFS_HELPER_H_
+
+#include <memory>
+#include <string>
+
+#include "base/macros.h"
+#include "components/prefs/scoped_user_pref_update.h"
+
+class PrefService;
+
+namespace base {
+class DictionaryValue;
+class FilePath;
+}
+
+// This class wraps a PrefService so that calls to get/set a preference value
+// apply to the value under the key for a specific storage partition.
+class ChromeZoomPrefsHelper {
+ public:
+  ChromeZoomPrefsHelper(PrefService* pref_service,
+                        const base::FilePath& profile_path,
+                        const base::FilePath& partition_path);
+
+  static std::string GetHashForTesting(const base::FilePath& relative_path);
+
+  // Get/set the value under our partition key for the pref.
+  bool GetBoolean(const char* pref_name, bool* value) const;
+  void SetBoolean(const char* pref_name, bool value);
+  bool GetDouble(const char* pref_name, double* value) const;
+  void SetDouble(const char* pref_name, double value);
+
+  // Get the dictionary under our partition key for the pref.
+  bool GetDictionary(const char* pref_name,
+                     const base::DictionaryValue** value) const;
+  // Get a DictionaryPrefUpdate for the pref which can then be used to get a
+  // mutable dictionary.
+  std::unique_ptr<DictionaryPrefUpdate> GetUpdate(const char* pref_name);
+  // Get a mutable dictionary under our partition key for the pref.
+  // |update| must outlive the use of the returned dictionary.
+  base::DictionaryValue* GetMutableDictionary(
+      DictionaryPrefUpdate* update) const;
+
+ private:
+  PrefService* pref_service_;
+  std::string partition_key_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChromeZoomPrefsHelper);
+};
+
+#endif  // CHROME_BROWSER_UI_ZOOM_CHROME_ZOOM_PREFS_HELPER_H_