Specify a default display UI scale to reset the zoom to

ui/display/manager/managed_display_info.h

 // Copyright (c) 2013 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 UI_DISPLAY_MANAGER_MANAGED_DISPLAY_INFO_H_
 #define UI_DISPLAY_MANAGER_MANAGED_DISPLAY_INFO_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 34 matching lines @@
 
   // Returns true if |other| has same size and scale factors.
   bool IsEquivalent(const scoped_refptr<ManagedDisplayMode>& other) const;
 
   const gfx::Size& size() const { return size_; }
   bool is_interlaced() const { return is_interlaced_; }
   float refresh_rate() const { return refresh_rate_; }
 
   bool native() const { return native_; }
 
+  bool is_default() const { return is_default_; }
+  void set_is_default(bool is_default) { is_default_ = is_default; }
+
   // Missing from ui::ManagedDisplayMode
   float ui_scale() const { return ui_scale_; }
   float device_scale_factor() const { return device_scale_factor_; }
 
  private:
   ~ManagedDisplayMode();
   friend class base::RefCounted<ManagedDisplayMode>;
 
   gfx::Size size_;             // Physical pixel size of the display.
   float refresh_rate_;         // Refresh rate of the display, in Hz.
   bool is_interlaced_;         // True if mode is interlaced.
   bool native_;                // True if mode is native mode of the display.
+  bool is_default_ = false;    // True if mode is one with default UI scale.
   float ui_scale_;             // The UI scale factor of the mode.
   float device_scale_factor_;  // The device scale factor of the mode.
 
   DISALLOW_COPY_AND_ASSIGN(ManagedDisplayMode);
 };
 
 // ManagedDisplayInfo contains metadata for each display. This is used to
 // create |display::Display| as well as to maintain extra infomation
 // to manage displays in ash environment.
 // This class is intentionally made copiable.
@@ skipping 282 matching lines @@
   // If you add a new member, you need to update Copy().
 };
 
 // Resets the synthesized display id for testing. This
 // is necessary to avoid overflowing the output index.
 void DISPLAY_EXPORT ResetDisplayIdForTest();
 
 }  // namespace display
 
 #endif  //  UI_DISPLAY_MANAGER_MANAGED_DISPLAY_INFO_H_