Desktop Aura: Allow tab drags out of window.

ui/base/event.h

Index: ui/base/event.h
diff --git a/ui/base/event.h b/ui/base/event.h
index 43fb253efb76b38a6d07e242a7759e709d3c5b6d..d7b2c2ce7f00610fd9214fc2ceea31fdbbf512be 100644
--- a/ui/base/event.h
+++ b/ui/base/event.h
@@ -136,6 +136,13 @@ class UI_EXPORT LocatedEvent : public Event {
   gfx::Point location() const { return location_; }
   gfx::Point root_location() const { return root_location_; }
 
+  bool valid_system_location() const { return valid_system_location_; }
+  void set_system_location(const gfx::Point& loc) {
+    valid_system_location_ = true;
+    system_location_ = loc;
+  }
+  const gfx::Point& system_location() const { return system_location_; }
+
   // Applies |root_transform| to the event.
   // This is applied to both |location_| and |root_location_|.
   virtual void UpdateForRootTransform(const Transform& root_transform);
@@ -150,7 +157,11 @@ class UI_EXPORT LocatedEvent : public Event {
   LocatedEvent(const LocatedEvent& model, T* source, T* target)
       : Event(model),
         location_(model.location_),
-        root_location_(model.root_location_) {
+        root_location_(model.root_location_),
+        valid_system_location_(model.valid_system_location_),
+        system_location_(model.system_location_) {
+    // TODO(erg): May need to create system_location_ by converting location to
+    // system coordinates here.
     if (target && target != source)
       T::ConvertPointToTarget(source, target, &location_);
   }
@@ -166,7 +177,14 @@ class UI_EXPORT LocatedEvent : public Event {
 
   gfx::Point location_;
 
+  // |location_| multiplied by an optional transformation matrix for
+  // rotations, animations and skews.
   gfx::Point root_location_;
+
+  // |location_| in underlying system screen coordinates. This can be invalid
+  // |during synthesized events if a location isn't explicitly set.
+  bool valid_system_location_;
+  gfx::Point system_location_;
 };
 
 class UI_EXPORT MouseEvent : public LocatedEvent {