Non passive touch end or touch cancel listeners should not block scroll.

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index bc494871089e4fd218ce9325b398887d61a9f8ad..b79dad54e46b803ff5d127db36e5a6b970073376 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -843,6 +843,17 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleTouchStart(
       touch_start_result_ == DROP_EVENT || result == DID_NOT_HANDLE)
     touch_start_result_ = result;
 
+  // If |result| is still DROP_EVENT look at the touch end handler as
+  // we may not want to discard the entire touch sequence. Note this
+  // code is explicitly after the assignment of the |touch_start_result_|
+  // so the touch moves are not sent to the main thread un-necessarily.
+  if (result == DROP_EVENT &&
+      input_handler_->GetEventListenerProperties(
+          cc::EventListenerClass::kTouchEndOrCancel) !=
+          cc::EventListenerProperties::kNone) {
+    result = DID_HANDLE_NON_BLOCKING;
+  }
+
   return result;
 }