Replaced synthetic MouseEvent in CustomButton::AcceleratorPressed() with just an Event.

ui/base/accelerators/accelerator.h

Index: ui/base/accelerators/accelerator.h
diff --git a/ui/base/accelerators/accelerator.h b/ui/base/accelerators/accelerator.h
index f5ee41709ccf41896dd6f2c49ebe26d79c0fa52d..b1904ac6529ae55aad371bfa35a54b54867ffde6 100644
--- a/ui/base/accelerators/accelerator.h
+++ b/ui/base/accelerators/accelerator.h
@@ -53,6 +53,8 @@ class UI_BASE_EXPORT Accelerator {
   // available modifier ones. This does not include EF_IS_REPEAT.
   static int MaskOutKeyEventFlags(int flags);
 
+  KeyEvent ToKeyEvent() const;
+
   Accelerator& operator=(const Accelerator& accelerator);
 
   // Define the < operator so that the KeyboardShortcut can be used as a key in