Implement link selection on alt+mouse drag.

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 414 matching lines @@
         newSelection.expandUsingGranularity(ParagraphGranularity);
     }
 
     return updateSelectionForMouseDownDispatchingSelectStart(innerNode, expandSelectionToRespectUserSelectAll(innerNode, newSelection), ParagraphGranularity);
 }
 
 void SelectionController::handleMousePressEvent(const MouseEventWithHitTestResults& event)
 {
     // If we got the event back, that must mean it wasn't prevented,
     // so it's allowed to start a drag or selection if it wasn't in a scrollbar.
-    m_mouseDownMayStartSelect = canMouseDownStartSelect(event.innerNode()) && !event.scrollbar();
+    m_mouseDownMayStartSelect = (canMouseDownStartSelect(event.innerNode()) || mayBeLinkSelection(event))
+        && !event.scrollbar();
     m_mouseDownWasSingleClickInSelection = false;
     // Avoid double-tap touch gesture confusion by restricting multi-click side
     // effects, e.g., word selection, to editable regions.
     m_mouseDownAllowsMultiClick = !event.event().fromTouch() || selection().hasEditableStyle();
 }
 
 void SelectionController::handleMouseDraggedEvent(const MouseEventWithHitTestResults& event, const IntPoint& mouseDownPos, const LayoutPoint& dragStartPos, Node* mousePressNode, const IntPoint& lastKnownMousePosition)
 {
     if (m_selectionState != SelectionState::ExtendedSelection) {
         HitTestRequest request(HitTestRequest::ReadOnly | HitTestRequest::Active);
@@ skipping 109 matching lines @@
 void SelectionController::sendContextMenuEvent(const MouseEventWithHitTestResults& mev, const LayoutPoint& position)
 {
     if (selection().contains(position)
         || mev.scrollbar()
         // FIXME: In the editable case, word selection sometimes selects content that isn't underneath the mouse.
         // If the selection is non-editable, we do word selection to make it easier to use the contextual menu items
         // available for text selections.  But only if we're above text.
         || !(selection().isContentEditable() || (mev.innerNode() && mev.innerNode()->isTextNode())))
         return;
 
-    m_mouseDownMayStartSelect = true; // context menu events are always allowed to perform a selection
+    // Context menu events are always allowed to perform a selection.
+    TemporaryChange<bool> mouseDownMayStartSelectChange(m_mouseDownMayStartSelect, true);
 
     if (mev.hitTestResult().isMisspelled())
         return selectClosestMisspellingFromMouseEvent(mev);
 
     if (!m_frame->editor().behavior().shouldSelectOnContextualMenuClick())
         return;
 
     selectClosestWordOrLinkFromMouseEvent(mev);
 }
 
@@ skipping 40 matching lines @@
         m_selectionState = SelectionState::PlacedCaret;
     else
         m_selectionState = SelectionState::HaveNotStartedSelection;
 }
 
 FrameSelection& SelectionController::selection() const
 {
     return m_frame->selection();
 }
 
+bool mayBeLinkSelection(const MouseEventWithHitTestResults& event)

[tkent, 2016/03/25 03:33:02]

This looks "isLinkSelection" to me.  Why "mayBe"?

+{
+    return event.event().altKey() && event.isOverLink();
+}
+
 } // namespace blink