Fix visible position calculation in accessible setSelection

third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp

 /*
 * Copyright (C) 2008 Apple 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
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 1955 matching lines @@
         return toAXLayoutObject(axObject);
 
     return nullptr;
 }
 
 
 //
 // Modify or take an action on an object.
 //
 
+// Convert from an accessible object and offset to a VisiblePosition.
+static VisiblePosition toVisiblePosition(AXObject* obj, int offset)
+{
+    // First walk up until we find an accessible object with an associated node.
+    AXObject* runner = obj;
+    Node* node = nullptr;
+    while (runner && !node) {
+        node = runner->getNode();
+        runner = runner->parentObject();
+    }
+
+    if (!node)
+        return VisiblePosition();
+
+    // If it's not a text node, no conversion is necessary, just create a VisiblePosition
+    // with this node and offset.
+    if (!node->isTextNode())
+        return createVisiblePosition(Position(node, offset));
+
+    // If it is a text node, we need to call some utility functions that use a TextIterator
+    // to walk the characters of the node and figure out the position corresponding to the
+    // visible character at position |offset|.
+    ContainerNode* parent = node->parentNode();
+    if (!parent)
+        return VisiblePosition();
+
+    VisiblePosition nodePosition = blink::visiblePositionBeforeNode(*node);
+    int nodeIndex = blink::indexForVisiblePosition(nodePosition, parent);
+    return blink::visiblePositionForIndex(nodeIndex + offset, parent);
+}
+
 void AXLayoutObject::setSelection(const AXRange& selection)
 {
     if (!getLayoutObject() || !selection.isValid())
         return;
 
     AXObject* anchorObject = selection.anchorObject ?
         selection.anchorObject.get() : this;
     AXObject* focusObject = selection.focusObject ?
         selection.focusObject.get() : this;
 
@@ skipping 11 matching lines @@
                 selection.anchorOffset, selection.focusOffset,
                 SelectionHasForwardDirection, NotDispatchSelectEvent);
         } else {
             textControl->setSelectionRange(
                 selection.focusOffset, selection.anchorOffset,
                 SelectionHasBackwardDirection, NotDispatchSelectEvent);
         }
         return;
     }
 
-    Node* anchorNode = nullptr;
-    while (anchorObject && !anchorNode) {
-        anchorNode = anchorObject->getNode();
-        anchorObject = anchorObject->parentObject();
-    }
-
-    Node* focusNode = nullptr;
-    while (focusObject && !focusNode) {
-        focusNode = focusObject->getNode();
-        focusObject = focusObject->parentObject();
-    }
-
-    if (!anchorNode || !focusNode)
-        return;
-
     LocalFrame* frame = getLayoutObject()->frame();
     if (!frame)
         return;
 
     // TODO(dglazkov): The use of updateStyleAndLayoutIgnorePendingStylesheets needs to be audited.
     // see http://crbug.com/590369 for more details.
     // This callsite should probably move up the stack.
     frame->document()->updateStyleAndLayoutIgnorePendingStylesheets();
 
     // Set the selection based on visible positions, because the offsets in accessibility nodes
     // are based on visible indexes, which often skips redundant whitespace, for example.
-    VisiblePosition anchorVisiblePosition = anchorNode->isTextNode()
-        ? blink::visiblePositionForIndex(selection.anchorOffset, anchorNode->parentNode())
-        : createVisiblePosition(Position(anchorNode, selection.anchorOffset));
-    VisiblePosition focusVisiblePosition = focusNode->isTextNode()
-        ? blink::visiblePositionForIndex(selection.focusOffset, focusNode->parentNode())
-        : createVisiblePosition(Position(focusNode, selection.focusOffset));
+    VisiblePosition anchorVisiblePosition = toVisiblePosition(anchorObject, selection.anchorOffset);
+    VisiblePosition focusVisiblePosition = toVisiblePosition(focusObject, selection.focusOffset);
+    if (anchorVisiblePosition.isNull() || focusVisiblePosition.isNull())
+        return;
+
     frame->selection().setSelection(VisibleSelection(anchorVisiblePosition, focusVisiblePosition));

[yosin_UTC9, 2016/07/27 07:36:37]

Could you pass |Position| instead of |VisiblePositon|?
Since |VisiblePosition| constructor attempts to update layout, we would like to
avoid to reduce usage of VisaiblePosition.

 }
 
 bool AXLayoutObject::isValidSelectionBound(const AXObject* boundObject) const
 {
     return getLayoutObject() && boundObject && !boundObject->isDetached()
         && boundObject->isAXLayoutObject() && boundObject->getLayoutObject()
         && boundObject->getLayoutObject()->frame() == getLayoutObject()->frame()
         && &boundObject->axObjectCache() == &axObjectCache();
 }
 
@@ skipping 520 matching lines @@
                     result.unite(labelRect);
                 }
             }
         }
     }
 
     return result;
 }
 
 } // namespace blink