Selection API: Selection.extend() should throw if rangeCount is 0.

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

Index: third_party/WebKit/Source/core/editing/DOMSelection.cpp
diff --git a/third_party/WebKit/Source/core/editing/DOMSelection.cpp b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
index 34c9a1c8e64719d26bfc41d5b133c9a5c5b780e6..4c937826c3254d9752547ddc99192218535456be 100644
--- a/third_party/WebKit/Source/core/editing/DOMSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
@@ -365,8 +365,11 @@ void DOMSelection::extend(Node* node,
                           ExceptionState& exceptionState) {
   DCHECK(node);
 
-  if (!isAvailable())
+  if (rangeCount() == 0) {
+    exceptionState.throwDOMException(
+        InvalidStateError, "This Selection object doesn't have any Ranges.");
     return;
+  }
 
   if (offset < 0) {
     exceptionState.throwDOMException(