Merge 181487 "Editing: Let Selection.collapse with null clears s..."

Source/core/editing/DOMSelection.cpp

Index: Source/core/editing/DOMSelection.cpp
===================================================================
--- Source/core/editing/DOMSelection.cpp	(revision 181787)
+++ Source/core/editing/DOMSelection.cpp	(working copy)
@@ -197,10 +197,14 @@
 
 void DOMSelection::collapse(Node* node, int offset, ExceptionState& exceptionState)
 {
-    ASSERT(node);
     if (!m_frame)
         return;
 
+    if (!node) {
+        m_frame->selection().clear();
+        return;
+    }
+
     if (offset < 0) {
         exceptionState.throwDOMException(IndexSizeError, String::number(offset) + " is not a valid offset.");
         return;