Implement array bounds checks explicitly in the optimized IL.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 11394)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -73,6 +73,13 @@
 }
 
 
+bool CheckArrayBoundComp::AttributesEqual(Computation* other) const {
+  CheckArrayBoundComp* other_check = other->AsCheckArrayBound();
+  if (other_check == NULL) return false;
+  return array_type() == other_check->array_type();
+}
+
+
 // Returns true if the value represents a constant.
 bool UseVal::BindsToConstant() const {
   BindInstr* bind = definition()->AsBind();
@@ -1096,6 +1103,11 @@
 }
 
 
+RawAbstractType* CheckArrayBoundComp::CompileType() const {
+  return AbstractType::null();
+}
+
+
 RawAbstractType* CheckEitherNonSmiComp::CompileType() const {
   return AbstractType::null();
 }