Add an identity (id) to system drag & drop.

Used for gears file drag & drop in chrome, assign a drag id (identity) to
each drag and drop session.

Send the identity to the renderer WebViewImpl in drag enter notifications,
provide a getter method.

BUG=7995

Original patch by noel.gordon@gmail.com in:
http://codereview.chromium.org/28108/show

Review URL: http://codereview.chromium.org/28158

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@10430 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 17 insertions, 0 deletions

diff --git a/base/base_drop_target.cc b/base/base_drop_target.cc
index 9809255..1dda396 100644
--- a/base/base_drop_target.cc
+++ b/base/base_drop_target.cc
@@ -11,6 +11,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 IDropTargetHelper* BaseDropTarget::cached_drop_target_helper_ = NULL;
+int32 BaseDropTarget::drag_identity_ = 0;
 
 BaseDropTarget::BaseDropTarget(HWND hwnd)
     : hwnd_(hwnd),
@@ -53,6 +54,11 @@ HRESULT BaseDropTarget::DragEnter(IDataObject* data_object,
     *effect = DROPEFFECT_NONE;
     return S_OK;
   }
+
+  // Update the drag identity, skipping 0.
+  if (++drag_identity_ == 0)
+    ++drag_identity_;
+
   current_data_object_ = data_object;
   POINT screen_pt = { cursor_position.x, cursor_position.y };
   *effect = OnDragEnter(current_data_object_, key_state, screen_pt, *effect);
diff --git a/base/base_drop_target.h b/base/base_drop_target.h
index 9f20752..cf63be28 100644
--- a/base/base_drop_target.h
+++ b/base/base_drop_target.h
@@ -85,6 +85,9 @@ class BaseDropTarget : public IDropTarget {
                        POINT cursor_position,
                        DWORD effect);
 
+  // Return the drag identity.
+  static int32 GetDragIdentity() { return drag_identity_; }
+
  private:
   // Returns the cached drop helper, creating one if necessary. The returned
   // object is not addrefed. May return NULL if the object couldn't be created.
@@ -103,6 +106,14 @@ class BaseDropTarget : public IDropTarget {
   // first time it is actually used.
   static IDropTargetHelper* cached_drop_target_helper_;
 
+  // The drag identity (id). An up-counter that increases when the cursor first
+  // moves over the HWND in a DnD session (OnDragEnter). 0 is reserved to mean
+  // the "no/unknown" identity, and is used for initialization. The identity is
+  // sent to the renderer in drag enter notifications. Note: the identity value
+  // is passed over the renderer NPAPI interface to gears, so use int32 instead
+  // of int here.
+  static int32 drag_identity_;
+
   // The HWND of the source. This HWND is used to determine coordinates for
   // mouse events that are sent to the renderer notifying various drag states.
   HWND hwnd_;