Fix build issue in Debug mode

Build error:
input_handler_proxy.cc:610:1: error: control reaches end of non-void
function [-Werror=return-type]

BUG=

Review URL: https://codereview.chromium.org/1631563002

Cr-Commit-Position: refs/heads/master@{#371523}

ui/events/blink/input_handler_proxy.cc

@@ -601,12 +601,11 @@ InputHandlerProxy::HandleGestureScrollUpdate(
       default:
         return DID_NOT_HANDLE;
     }
-  } else {
-    cc::InputHandlerScrollResult scroll_result =
-        input_handler_->ScrollBy(&scroll_state);
-    HandleOverscroll(scroll_point, scroll_result);
-    return scroll_result.did_scroll ? DID_HANDLE : DROP_EVENT;
   }
+  cc::InputHandlerScrollResult scroll_result =
+      input_handler_->ScrollBy(&scroll_state);
+  HandleOverscroll(scroll_point, scroll_result);
+  return scroll_result.did_scroll ? DID_HANDLE : DROP_EVENT;
 }
 
 InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureScrollEnd(