Drag and drop cleans up touch sequences from the source window.

ui/events/gestures/gesture_recognizer.h

Index: ui/events/gestures/gesture_recognizer.h
diff --git a/ui/events/gestures/gesture_recognizer.h b/ui/events/gestures/gesture_recognizer.h
index 245685257ba215cdc4609b7cb73404f97a17df00..5d7b792980f39d12c586e5aeadfb9f6ec0a2287d 100644
--- a/ui/events/gestures/gesture_recognizer.h
+++ b/ui/events/gestures/gesture_recognizer.h
@@ -62,14 +62,18 @@ class EVENTS_EXPORT GestureRecognizer {
   // |not_cancelled| == nullptr, cancels all touches.
   virtual void CancelActiveTouchesExcept(GestureConsumer* not_cancelled) = 0;
 
-  // Makes |new_consumer| the target for events previously targeting
-  // |current_consumer|. Touches targeting all other targets are
-  // canceled. The caller is responsible for updating the state of the
-  // consumers to be aware of this transfer of control (there are no
-  // ENTERED/EXITED events).
-  virtual void TransferEventsTo(GestureConsumer* current_consumer,
+  // Transfer the gesture stream from the drag source (current_consumer) to the
+  // consumer used for dragging (new_consumer). This dispatches cancel events to
+  // |current_consumer| to ensure that its touch stream remains valid.
+  virtual void BeginDragAndDrop(GestureConsumer* current_consumer,
                                 GestureConsumer* new_consumer) = 0;
 
+  // Transfer the gesture stream from the drag source (current_consumer) to the
+  // consumer used for dragging (new_consumer). This doesn't dispatch cancel
+  // events to |current_consumer|.
+  virtual void BeginTabDrag(GestureConsumer* current_consumer,

[sky, 2016/05/12 15:43:34]

This code sits lower in the stack than the tab dragging code. So using 'tab' in
the name feels wrong. Did you consider combining BeginDragAndDrop and
BeginTabDrag and making the combined function take a parameter indicating if the
events should be canceled?

+                            GestureConsumer* new_consumer) = 0;
+
   // If a gesture is underway for |consumer| |point| is set to the last touch
   // point and true is returned. If no touch events have been processed for
   // |consumer| false is returned and |point| is untouched.