aura: Track mouse button state.

ui/aura/desktop.h

Index: ui/aura/desktop.h
diff --git a/ui/aura/desktop.h b/ui/aura/desktop.h
index 5f455ffccac0fd2bbf92c07d2c04a466b426c1ac..8ba752a5778a636f530016c4533eac1bbd2ceab2 100644
--- a/ui/aura/desktop.h
+++ b/ui/aura/desktop.h
@@ -122,6 +122,9 @@ class AURA_EXPORT Desktop : public ui::CompositorDelegate,
   void AddObserver(DesktopObserver* observer);
   void RemoveObserver(DesktopObserver* observer);
 
+  // Are any mouse buttons currently down?
+  bool IsMouseButtonDown() const;
+
   // Capture -------------------------------------------------------------------
 
   // Sets capture to the specified window.
@@ -192,6 +195,9 @@ class AURA_EXPORT Desktop : public ui::CompositorDelegate,
   // Last location seen in a mouse event.
   gfx::Point last_mouse_location_;
 
+  // ui::EventFlags containing the current state of the mouse buttons.
+  int mouse_button_flags_;
+
   // Last cursor set.  Used for testing.
   gfx::NativeCursor last_cursor_;