Force events to be non blocking if main thread is unresponsive.

third_party/WebKit/public/platform/WebInputEvent.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 179 matching lines @@
     // The set of non-stateful modifiers that specifically change the
     // interpretation of the key being pressed. For example; IsLeft,
     // IsRight, IsComposing don't change the meaning of the key
     // being pressed. NumLockOn, ScrollLockOn, CapsLockOn are stateful
     // and don't indicate explicit depressed state.
     KeyModifiers =
         SymbolKey | FnKey | AltGrKey | MetaKey | AltKey | ControlKey | ShiftKey,
   };
 
   // Indicates whether the browser needs to block on the ACK result for
-  // this event, and if not why note (for metrics/diagnostics purposes).
+  // this event, and if not, why (for metrics/diagnostics purposes).
   // These values are direct mappings of the values in PlatformEvent
   // so the values can be cast between the enumerations. static_asserts
   // checking this are in web/WebInputEventConversion.cpp.
   enum DispatchType {
     // Event can be canceled.
     Blocking,
     // Event can not be canceled.
     EventNonBlocking,
     // All listeners are passive; not cancelable.
     ListenersNonBlockingPassive,
     // This value represents a state which would have normally blocking
     // but was forced to be non-blocking during fling; not cancelable.
     ListenersForcedNonBlockingDueToFling,
+    // This value represents a state which would have normally blocking but
+    // was forced to be non-blocking due to the main thread being
+    // unresponsive.
+    ListenersForcedNonBlockingDueToMainThreadResponsiveness,
   };
 
   // The rail mode for a wheel event specifies the axis on which scrolling is
   // expected to stick. If this axis is set to Free, then scrolling is not
   // stuck to any axis.
   enum RailsMode {
     RailsModeFree = 0,
     RailsModeHorizontal = 1,
     RailsModeVertical = 2,
   };
@@ skipping 271 matching lines @@
         movedBeyondSlopRegion(false),
         touchStartOrFirstTouchMove(false),
         uniqueTouchEventId(0) {}
 };
 
 #pragma pack(pop)
 
 }  // namespace blink
 
 #endif