Reverting r12383, caused a build breakage on all platforms.

chrome/views/controls/button/custom_button.cc

Index: chrome/views/controls/button/custom_button.cc
===================================================================
--- chrome/views/controls/button/custom_button.cc	(revision 12384)
+++ chrome/views/controls/button/custom_button.cc	(working copy)
@@ -82,14 +82,13 @@
 CustomButton::CustomButton(ButtonListener* listener)
     : Button(listener),
       state_(BS_NORMAL),
-      animate_on_state_change_(true),
-      triggerable_event_flags_(MouseEvent::EF_LEFT_BUTTON_DOWN) {
+      animate_on_state_change_(true) {
   hover_animation_.reset(new ThrobAnimation(this));
   hover_animation_->SetSlideDuration(kHoverFadeDurationMs);
 }
 
 bool CustomButton::IsTriggerableEvent(const MouseEvent& e) {
-  return (triggerable_event_flags_ & e.GetFlags()) != 0;
+  return e.IsLeftMouseButton();
 }
 
 ////////////////////////////////////////////////////////////////////////////////