Selecting with shift+drag results in unexpected drag-n-drop

third_party/WebKit/Source/core/editing/SelectionController.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 110 matching lines @@
 
 bool SelectionController::handleMousePressEventSingleClick(const MouseEventWithHitTestResults& event)
 {
     TRACE_EVENT0("blink", "SelectionController::handleMousePressEventSingleClick");
 
     m_frame->document()->updateStyleAndLayoutIgnorePendingStylesheets();
     Node* innerNode = event.innerNode();
     if (!(innerNode && innerNode->layoutObject() && m_mouseDownMayStartSelect))
         return false;
 
-    // Extend the selection if the Shift key is down, unless the click is in a link.
-    bool extendSelection = event.event().shiftKey() && !event.isOverLink();
+    // Extend the selection if the Shift key is down, unless the click is in a link or image.
+    bool extendSelection = isExtendingSelection(event);
 
     // Don't restart the selection when the mouse is pressed on an
     // existing selection so we can allow for text dragging.
     if (FrameView* view = m_frame->view()) {
         LayoutPoint vPoint = view->rootFrameToContents(event.event().position());
         if (!extendSelection && selection().contains(vPoint)) {
             m_mouseDownWasSingleClickInSelection = true;
             return false;
         }
     }
@@ skipping 485 matching lines @@
 FrameSelection& SelectionController::selection() const
 {
     return m_frame->selection();
 }
 
 bool isLinkSelection(const MouseEventWithHitTestResults& event)
 {
     return event.event().altKey() && event.isOverLink();
 }
 
+bool isExtendingSelection(const MouseEventWithHitTestResults& event)
+{
+    DCHECK_LE(event.event().clickCount(), 1);
+

[yosin_UTC9, 2016/06/08 01:37:21]

nit: no need to have an extra blank line here.

[tonikitoo, 2016/06/24 18:39:20]

The assert was not actually right. I removed it.

+    bool isMouseDownOnLinkOrImage = event.isOverLink() || event.hitTestResult().image();
+    return event.event().shiftKey() && !isMouseDownOnLinkOrImage;
+}
+
 } // namespace blink