Fix crash when InkDropHostView::SetHasInkDrop() is called multiple times

ui/views/animation/ink_drop_host_view.cc

Index: ui/views/animation/ink_drop_host_view.cc
diff --git a/ui/views/animation/ink_drop_host_view.cc b/ui/views/animation/ink_drop_host_view.cc
index e6b1e424155d41e75056cdf1744fc2e7e2684fcc..acba512f0b23e5e95260e39b19f96abc78708e87 100644
--- a/ui/views/animation/ink_drop_host_view.cc
+++ b/ui/views/animation/ink_drop_host_view.cc
@@ -39,6 +39,8 @@ const int InkDropHostView::kInkDropSmallCornerRadius = 2;
 // An EventHandler that is guaranteed to be invoked and is not prone to
 // InkDropHostView descendents who do not call
 // InkDropHostView::OnGestureEvent().
+// Only one instance of this class can exist at any given time. Make sure to
+// delete the old one, if any, *before* instantiating a new one.

[sadrul, 2016/06/26 03:51:31]

You mean only one instance can exist *for a particular host_view*, right?

[mohsen, 2016/06/27 18:59:10]

Right. Updated the comment.

 //
 // TODO(bruthig): Consider getting rid of this class.
 class InkDropHostView::InkDropGestureHandler : public ui::EventHandler {
@@ -221,11 +223,11 @@ bool InkDropHostView::ShouldShowInkDropForFocus() const {
 }
 
 void InkDropHostView::SetHasInkDrop(bool has_an_ink_drop) {
+  gesture_handler_.reset();
   if (has_an_ink_drop) {
     ink_drop_.reset(new InkDropImpl(this));
     gesture_handler_.reset(new InkDropGestureHandler(this, ink_drop_.get()));

[sadrul, 2016/06/26 03:51:31]

Add a comment here that any existing InkDropGestureHandler instance needs to be
destroyed first, before a new instance is created.

But, instead of recreating gesture_handler_, if it's non-null, can you just
change its |ink_drop_|? e.g. InkDropGestureHandler::SetInkDrop(...)

[mohsen, 2016/06/27 18:59:10]

Yes, Added SetInkDrop().

   } else {
-    gesture_handler_.reset();
     ink_drop_.reset(new InkDropStub());
   }
 }