Desktop aura: Break aura::Window::SetParent in two.

ui/aura/window.h

 // Copyright (c) 2012 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_AURA_WINDOW_H_
 #define UI_AURA_WINDOW_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 153 matching lines @@
   // Returns the target bounds of the window. If the window's layer is
   // not animating, it simply returns the current bounds.
   gfx::Rect GetTargetBounds() const;
 
   // Marks the a portion of window as needing to be painted.
   void SchedulePaintInRect(const gfx::Rect& rect);
 
   // Assigns a new external texture to the window's layer.
   void SetExternalTexture(ui::Texture* texture);
 
-  // Sets the parent window of the window. If NULL, the window is parented to
-  // the root window.
-  void SetParent(Window* parent);
+  // Sets the parent window of the window. Can not be NULL.

[Ben Goodger (Google), 2012/11/20 23:46:38]

Cannot or Must not

+  void SetParentTo(Window* parent);
+
+  // Attach this window somewhere.
+  //
+  // |context_root| can never be NULL; since desktop aura and ash can be run at

[Ben Goodger (Google), 2012/11/20 23:46:38]

Don't leak knowledge of downstream components into an upstream comment.

// |target_root| must not be NULL.
void SetDefaultParentByTargetRoot(RootWindow* target_root);

+  // the same time in the same process, we always must have some context to
+  // determine desktop vs ash semantics. Users shouldn't assume that the window
+  // will be rooted to |context_root|.
+  void SetDefaultParentByTargetRoot(RootWindow* context_root);
 
   // Stacks the specified child of this Window at the front of the z-order.
   void StackChildAtTop(Window* child);
 
   // Stacks |child| above |target|.  Does nothing if |child| is already above
   // |target|.  Does not stack on top of windows with NULL layer delegates,
   // see WindowTest.StackingMadrigal for details.
   void StackChildAbove(Window* child, Window* target);
 
   // Stacks |child| below |target|. Does nothing if |child| is already below
@@ skipping 313 matching lines @@
   };
 
   std::map<const void*, Value> prop_map_;
 
   DISALLOW_COPY_AND_ASSIGN(Window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_H_