Enable touch-initiated drag-drop work on Windows

ui/base/dragdrop/drag_source_win.cc

Index: ui/base/dragdrop/drag_source_win.cc
diff --git a/ui/base/dragdrop/drag_source_win.cc b/ui/base/dragdrop/drag_source_win.cc
index 90ce68273a3379b463e1d9571d9fc73dbd26ad3f..756aed75b37634e25056d9f6e36106e4531f079a 100644
--- a/ui/base/dragdrop/drag_source_win.cc
+++ b/ui/base/dragdrop/drag_source_win.cc
@@ -6,7 +6,13 @@
 
 namespace ui {
 
-DragSourceWin::DragSourceWin() : cancel_drag_(false) {
+DragSourceWin::DragSourceWin()

[dcheng, 2013/05/28 20:34:02]

Nit: do we need this or can we just force all locations that instantiate this
class to be explicit?

[Hongbo Min, 2013/05/29 06:08:04]

I prefer to reserve it since it is unnecessary to change other code. This patch
is something specific HTML5 drag-drop by touch.

If the usage of DragSourceWin also has the same problem as HTML5 drag-drop, we
could remove it in future.

+    : cancel_drag_(false),
+      event_source_(DragDropTypes::DRAG_EVENT_SOURCE_MOUSE) {
+}
+
+DragSourceWin::DragSourceWin(DragDropTypes::DragEventSource event_source)
+    : cancel_drag_(false), event_source_(event_source) {
 }
 
 HRESULT DragSourceWin::QueryContinueDrag(BOOL escape_pressed, DWORD key_state) {
@@ -18,7 +24,12 @@ HRESULT DragSourceWin::QueryContinueDrag(BOOL escape_pressed, DWORD key_state) {
     return DRAGDROP_S_CANCEL;
   }
 
-  if (!(key_state & MK_LBUTTON)) {
+  // On Windows, the touch-initiated drag-drop is driven by mouse right down
+  // event programmatically.
+  if ((event_source_ == DragDropTypes::DRAG_EVENT_SOURCE_MOUSE &&
+      !(key_state & MK_LBUTTON)) ||
+      (event_source_ == DragDropTypes::DRAG_EVENT_SOURCE_TOUCH &&
+      !(key_state && MK_RBUTTON))) {
     OnDragSourceDrop();
     return DRAGDROP_S_DROP;
   }