Make sure we throw the right NSM error when indexing out of range of a variable that can be null.

sdk/lib/_internal/compiler/implementation/ssa/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/nodes.dart	(revision 27429)
+++ sdk/lib/_internal/compiler/implementation/ssa/nodes.dart	(working copy)
@@ -1244,12 +1244,14 @@
    */
   int staticChecks = FULL_CHECK;
 
-  HBoundsCheck(length, index) : super(<HInstruction>[length, index]) {
+  HBoundsCheck(length, index, array)
+      : super(<HInstruction>[length, index, array]) {
     instructionType = HType.INTEGER;
   }
 
   HInstruction get length => inputs[1];
   HInstruction get index => inputs[0];
+  HInstruction get array => inputs[2];
   bool isControlFlow() => true;
 
   accept(HVisitor visitor) => visitor.visitBoundsCheck(this);