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

third_party/WebKit/public/platform/WebInputEvent.h

Index: third_party/WebKit/public/platform/WebInputEvent.h
diff --git a/third_party/WebKit/public/platform/WebInputEvent.h b/third_party/WebKit/public/platform/WebInputEvent.h
index 43349d55392bfd07fde5960bfb8649effe5b3696..bbe7f34bb723f2949d203bcb2fb5b991c3a50fe2 100644
--- a/third_party/WebKit/public/platform/WebInputEvent.h
+++ b/third_party/WebKit/public/platform/WebInputEvent.h
@@ -198,7 +198,7 @@ class WebInputEvent {
   };
 
   // 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.
@@ -212,6 +212,10 @@ class WebInputEvent {
     // 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