Set the unique_event_id when converting from TouchEvent to WebTouchEvent

ui/events/base_event_utils.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/events/base_event_utils.h"
+
+#include "base/atomic_sequence_num.h"
+#include "base/logging.h"
+
+namespace ui {
+
+base::StaticAtomicSequenceNumber g_next_event_id;
+
+uint32 GetNextTouchEventId() {
+  // Set the first touch event ID to 1 because we set id to 0 for other types
+  // of events.
+  uint32 id = g_next_event_id.GetNext();
+  if (id == 0)
+    id = g_next_event_id.GetNext();
+  DCHECK_NE(0U, id);
+  return id;
+}
+
+}  // namespace ui
+