Enable MD by default on Windows for Canary/Dev and local builds.

ui/base/material_design/material_design_controller.h

 // Copyright 2015 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_BASE_MATERIAL_DESIGN_MATERIAL_DESIGN_CONTROLLER_H_
 #define UI_BASE_MATERIAL_DESIGN_MATERIAL_DESIGN_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "ui/base/ui_base_export.h"
 
@@ skipping 24 matching lines @@
   static Mode GetMode();
 
   // Returns true if the current mode is a material design variant.
   static bool IsModeMaterial();
 
   // Returns true if the current mode is a material design variant and this mode
   // should be extended to cover secondary UI.
   static bool IsSecondaryUiMaterial();
 
   // Returns the per-platform default material design variant.
   static Mode DefaultMode();

[sky, 2016/05/13 15:49:56]

sorry, random question. Can this be private?

[Peter Kasting, 2016/05/16 19:53:16]

It's called elsewhere only by tests.  I think it's better to restrict access to
it to just testing, so I did so.

 
+  // On Windows, this should be called during startup before anyone calls any of
+  // the functions above to declare whether we should default to Material mode.
+  // TODO(pkasting): Remove this as soon as MD is on by default.
+  static void SetDefaultToMaterial(bool default_to_material);

[sky, 2016/05/13 15:49:56]

I find it mildly confusing that you expect this function to be called before
initialize. Did you consider naming this InitializeWithDefault?

[Peter Kasting, 2016/05/16 19:53:16]

You mean, by combining its functionality with Initialize()?  That's a good idea,
and will remove the need for the static variable.  Done.

+
  private:
   friend class test::MaterialDesignControllerTestAPI;
 
   // Tracks whether |mode_| has been initialized. This is necessary so tests can
   // reset the state back to a clean state during tear down.
   static bool is_mode_initialized_;
 
+  // True if we should default to Material mode.  Only respected on Windows.
+  static bool default_to_material_;
+
   // The current Mode to be used by the system.
   static Mode mode_;
 
   // True when |mode_| applies beyond the primary UI (toolbar, tabstrip,
   // etc.). For example, this controls use of MD inside bubbles and dialogs.
   static bool include_secondary_ui_;
 
   // Declarations only. Do not allow construction of an object.
   MaterialDesignController();
   ~MaterialDesignController();
 
   // Resets the initialization state to uninitialized. To be used by tests to
   // allow calling Initialize() more than once.
   static void Uninitialize();
 
   // Set |mode_| to |mode| and updates |is_mode_initialized_| to true. Can be
   // used by tests to directly set the mode.
   static void SetMode(Mode mode);
 
   DISALLOW_COPY_AND_ASSIGN(MaterialDesignController);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_MATERIAL_DESIGN_MATERIAL_DESIGN_CONTROLLER_H_