Add create note palette action.

ash/common/system/chromeos/palette/palette_tool.h

 // Copyright 2016 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 ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_TOOL_H_
 #define ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_TOOL_H_
 
 #include <map>
 #include <memory>
 #include <vector>
@@ skipping 58 matching lines @@
 
   // Called when the user activates the tool. Only one tool per group can be
   // active at any given time.
   virtual void OnEnable();
 
   // Disable the tool, either because this tool called DisableSelf(), the
   // user cancelled the tool, or the user activated another tool within the
   // same group.
   virtual void OnDisable();
 
-  // Create a view that will be used in the palette. The view is owned by the
-  // caller. OnViewDestroyed is called when the view has been deallocated by its
-  // owner.
+  // Create a view that will be used in the palette, or nullptr if this tool
+  // should not be displayed. The view is owned by the caller. OnViewDestroyed
+  // is called when the view has been deallocated by its owner.
   virtual views::View* CreateView() = 0;
   virtual void OnViewDestroyed() = 0;
 
   // Returns an icon to use in the tray if this tool is active. Only one tool
   // (per-group) should ever have an active icon at any given time.
   virtual gfx::VectorIconId GetActiveTrayIcon();
 
  protected:
   // Enables/disables the tool.
   bool enabled() const { return enabled_; }
 
   Delegate* delegate() { return delegate_; }
 
  private:
   bool enabled_ = false;
 
   // Unowned pointer to the delegate. The delegate should outlive this instance.
   Delegate* delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(PaletteTool);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_TOOL_H_