Notify Blink about start of gesture scroll through a queued event.

blimp/net/input_message_generator.cc

Index: blimp/net/input_message_generator.cc
diff --git a/blimp/net/input_message_generator.cc b/blimp/net/input_message_generator.cc
index cfdc7c89c42c9a08bbae3ab684d5ed68c3974b36..195def3a8a880609d5256c0c0af2e7e3e9f11315 100644
--- a/blimp/net/input_message_generator.cc
+++ b/blimp/net/input_message_generator.cc
@@ -170,6 +170,7 @@ std::unique_ptr<BlimpMessage> InputMessageGenerator::GenerateMessage(
     case blink::WebInputEvent::Type::TouchMove:
     case blink::WebInputEvent::Type::TouchEnd:
     case blink::WebInputEvent::Type::TouchCancel:
+    case blink::WebInputEvent::Type::TouchScrollStarted:
       NOTIMPLEMENTED();
       return nullptr;
   }