[MacViews] Enable dragging a window by its caption/draggable areas.

ui/views/cocoa/views_nswindow_delegate.h

Index: ui/views/cocoa/views_nswindow_delegate.h
diff --git a/ui/views/cocoa/views_nswindow_delegate.h b/ui/views/cocoa/views_nswindow_delegate.h
index ec8e6e1378d33c432990b692646094314d6c4cd3..2f8449125324a539fa704608dc2382d549f068ec 100644
--- a/ui/views/cocoa/views_nswindow_delegate.h
+++ b/ui/views/cocoa/views_nswindow_delegate.h
@@ -52,6 +52,13 @@ class BridgedNativeWidget;
          returnCode:(NSInteger)returnCode
         contextInfo:(void*)contextInfo;
 
+// Called when the application receives a mouse-down, but before the event
+// is processed by NSWindows. Returns NO if the event should be processed as-is,
+// or YES if the event should be reposted to handle window dragging. Events are
+// reposted at the CGSessionEventTap level because window dragging happens there
+// before the application receives the event.
+- (BOOL)shouldRepostPendingLeftMouseDown:(NSPoint)locationInWindow;
+
 @end
 
 #endif  // UI_VIEWS_COCOA_VIEWS_NSWINDOW_DELEGATE_H_