firstRectForCharacterRange(): don't fall over in an editable-less frame.

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 1060 matching lines @@
 {
     return frame()->inputMethodController().compositionRange();
 }
 
 bool WebLocalFrameImpl::firstRectForCharacterRange(unsigned location, unsigned length, WebRect& rectInViewport) const
 {
     if ((location + length < location) && (location + length))
         length = 0;
 
     Element* editable = frame()->selection().rootEditableElementOrDocumentElement();
-    ASSERT(editable);
+    if (!editable)
+        return false;
     RefPtrWillBeRawPtr<Range> range = PlainTextRange(location, location + length).createRange(*editable);
     if (!range)
         return false;
     IntRect intRect = frame()->editor().firstRectForRange(range.get());
     rectInViewport = WebRect(intRect);
     rectInViewport = frame()->view()->contentsToViewport(rectInViewport);
     return true;
 }
 
 size_t WebLocalFrameImpl::characterIndexForPoint(const WebPoint& pointInViewport) const
@@ skipping 998 matching lines @@
 {
     m_frameWidget = frameWidget;
 }
 
 WebFrameWidgetImpl* WebLocalFrameImpl::frameWidget() const
 {
     return m_frameWidget;
 }
 
 } // namespace blink