Add new API for only moving the selection extent point.

Source/web/WebLocalFrameImpl.cpp

 /*
  * Copyright (C) 2009 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1144 matching lines @@
 {
     moveRangeSelection(base, extent);
 }
 
 void WebLocalFrameImpl::selectRange(const WebRange& webRange)
 {
     if (RefPtrWillBeRawPtr<Range> range = static_cast<PassRefPtrWillBeRawPtr<Range> >(webRange))
         frame()->selection().setSelectedRange(range.get(), VP_DEFAULT_AFFINITY, FrameSelection::NonDirectional, NotUserTriggered);
 }
 
+void WebLocalFrameImpl::moveRangeSelectionExtent(const WebPoint& point)
+{
+    VisibleSelection currentSelection = frame()->selection().selection();
+
+    VisiblePosition basePosition = currentSelection.isBaseFirst() ?
+        currentSelection.visibleStart() : currentSelection.visibleEnd();
+    VisiblePosition extentPosition = visiblePositionForWindowPoint(point);
+
+    // Prevent the selection from collapsing.

[mlamouri (slow - plz ping), 2014/10/18 08:43:52]

nit: could that be expressed in the WebLocalFrame.h declaration comment?

+    if (comparePositions(basePosition, extentPosition) == 0)
+        return;
+
+    VisibleSelection newSelection = VisibleSelection(basePosition, extentPosition);
+    frame()->selection().setSelection(newSelection, CharacterGranularity);
+}
+
 void WebLocalFrameImpl::moveRangeSelection(const WebPoint& base, const WebPoint& extent)
 {
     VisiblePosition basePosition = visiblePositionForWindowPoint(base);
     VisiblePosition extentPosition = visiblePositionForWindowPoint(extent);
     VisibleSelection newSelection = VisibleSelection(basePosition, extentPosition);
     frame()->selection().setSelection(newSelection, CharacterGranularity);
 }
 
 void WebLocalFrameImpl::moveCaretSelection(const WebPoint& point)
 {
@@ skipping 742 matching lines @@
 
 void WebLocalFrameImpl::invalidateAll() const
 {
     ASSERT(frame() && frame()->view());
     FrameView* view = frame()->view();
     view->invalidateRect(view->frameRect());
     invalidateScrollbar();
 }
 
 } // namespace blink