Set the unique_event_id when converting from TouchEvent to WebTouchEvent

content/browser/renderer_host/input/touch_emulator.cc

Index: content/browser/renderer_host/input/touch_emulator.cc
diff --git a/content/browser/renderer_host/input/touch_emulator.cc b/content/browser/renderer_host/input/touch_emulator.cc
index ed9134b1d6b1b853d2e24d8ab59bcb503d047f15..8388e09e33700d70ff1472c3e59dc9274438e8b1 100644
--- a/content/browser/renderer_host/input/touch_emulator.cc
+++ b/content/browser/renderer_host/input/touch_emulator.cc
@@ -11,6 +11,7 @@
 #include "content/public/common/content_client.h"
 #include "content/public/common/content_switches.h"
 #include "third_party/WebKit/public/platform/WebCursorInfo.h"
+#include "ui/events/base_event_utils.h"
 #include "ui/events/blink/blink_event_util.h"
 #include "ui/events/gesture_detection/gesture_provider_config_helper.h"
 #include "ui/gfx/image/image.h"
@@ -225,6 +226,7 @@ bool TouchEmulator::HandleTouchEvent(const blink::WebTouchEvent& event) {
 
 void TouchEmulator::HandleEmulatedTouchEvent(blink::WebTouchEvent event) {
   DCHECK(gesture_provider_);
+  event.uniqueTouchEventId = ui::GetNextTouchEventId();

[sadrul, 2015/04/23 16:56:23]

Should this happen in WebTouchEventTraits::ResetTypeAndTouchStates() instead?

[lanwei, 2015/04/24 20:21:09]

Tim pointed out that ResetTypeAndTouchStates may be called multiple times and
HandleEmulatedTouchEvent will only be called once, so it is safe to put it here.
We add this setting uniqueTouchEventId here is because this MotionEventWeb
object is generated from WebTouchEvent object which does not have a valid
uniqueTouchEventId. Normally WebTouchEvent are generated from MotionEvent which
are from TouchEvent, which will have a valid uniqueTouchEventId.

[tdresser, 2015/04/27 14:02:24]

Currently we only call ResetTypeAndTouchStates once per event, but I can picture
us introducing bugs by later calling ResetTypeAndTouchStates multiple times. It
seems unlikely that we'd switch to calling HandleEmulatedTouchEvent multiple
times per event.

We could move this to ResetTypeAndTouchStates, and DCHECK that the
uniqueTouchEventId is unset before generating a new one, but this seems more
straight forward to me.

   auto result = gesture_provider_->OnTouchEvent(MotionEventWeb(event));
   if (!result.succeeded)
     return;