Fix a crash that happens if a tab is closed while

base/base_drag_source.h

Index: base/base_drag_source.h
diff --git a/base/base_drag_source.h b/base/base_drag_source.h
index dea89aff0228813a8806237d34f57dfe6d49558d..3a4a94cd1cd8a0c380c5582a52f0c5e31f2ce439 100644
--- a/base/base_drag_source.h
+++ b/base/base_drag_source.h
@@ -23,6 +23,13 @@ class BaseDragSource : public IDropSource {
   BaseDragSource();
   virtual ~BaseDragSource() { }
 
+  // Stop the drag operation at the next chance we get.  This doesn't
+  // synchronously stop the drag (since Windows is controlling that),
+  // but lets us tell Windows to cancel the drag the next chance we get.
+  void CancelDrag() {
+    cancel_drag_ = true;
+  }
+
   // IDropSource implementation:
   HRESULT __stdcall QueryContinueDrag(BOOL escape_pressed, DWORD key_state);
   HRESULT __stdcall GiveFeedback(DWORD effect);
@@ -40,6 +47,9 @@ class BaseDragSource : public IDropSource {
  private:
   LONG ref_count_;
 
+  // Set to true if we want to cancel the drag operation.
+  bool cancel_drag_;
+
   DISALLOW_EVIL_CONSTRUCTORS(BaseDragSource);
 };