Implement link selection on alt+mouse drag.

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

Index: third_party/WebKit/Source/core/editing/SelectionController.cpp
diff --git a/third_party/WebKit/Source/core/editing/SelectionController.cpp b/third_party/WebKit/Source/core/editing/SelectionController.cpp
index e26e1732d57ef92bb4111b2507ed4856c894f2d5..df6b0ccabfb4950a5d61949b1d4f27119b6fd98c 100644
--- a/third_party/WebKit/Source/core/editing/SelectionController.cpp
+++ b/third_party/WebKit/Source/core/editing/SelectionController.cpp
@@ -432,7 +432,8 @@ void SelectionController::handleMousePressEvent(const MouseEventWithHitTestResul
 {
     // 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.
@@ -562,7 +563,8 @@ void SelectionController::sendContextMenuEvent(const MouseEventWithHitTestResult
         || !(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);