Implement WebContentsView::GetDropData for Mac; disable on Aura

content/browser/web_contents/web_contents_view_mac.mm

Index: content/browser/web_contents/web_contents_view_mac.mm
diff --git a/content/browser/web_contents/web_contents_view_mac.mm b/content/browser/web_contents/web_contents_view_mac.mm
index 15c704949e168471bc1e7bc44c0619f6638ed477..3e2677eda078e8c07fb3c082bdf06f2c00cb3f63 100644
--- a/content/browser/web_contents/web_contents_view_mac.mm
+++ b/content/browser/web_contents/web_contents_view_mac.mm
@@ -46,6 +46,7 @@ COMPILE_ASSERT_MATCHING_ENUM(DragOperationEvery);
 - (id)initWithWebContentsViewMac:(WebContentsViewMac*)w;
 - (void)registerDragTypes;
 - (void)setCurrentDragOperation:(NSDragOperation)operation;
+- (WebDropData*)dropData;
 - (void)startDragWithDropData:(const WebDropData&)dropData
             dragOperationMask:(NSDragOperation)operationMask
                         image:(NSImage*)image
@@ -248,7 +249,7 @@ void WebContentsViewMac::CancelDragAndCloseTab() {
 }
 
 WebDropData* WebContentsViewMac::GetDropData() const {
-  return NULL;
+  return [cocoa_view_ dropData];
 }
 
 void WebContentsViewMac::UpdateDragCursor(WebDragOperation operation) {
@@ -442,6 +443,10 @@ void WebContentsViewMac::CloseTab() {
   [dragDest_ setCurrentOperation:operation];
 }
 
+- (WebDropData*)dropData {
+  return [dragDest_ currentDropData];
+}
+
 - (WebContentsImpl*)webContents {
   if (webContentsView_ == NULL)
     return NULL;