Improve optimization of operations on indexables by using more inferred type information and by dis…

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

Index: sdk/lib/_internal/compiler/implementation/ssa/types.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/types.dart b/sdk/lib/_internal/compiler/implementation/ssa/types.dart
index e6a90448d03f18e4d4a77746e5f89787ce3062fa..93dfcd89251567cbf9a719c68ccb08e131bfbcef 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/types.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/types.dart
@@ -197,10 +197,15 @@ abstract class HType {
   // TODO(kasperl): Get rid of this one.
   bool isIndexablePrimitive() => false;
 
-  bool isIndexable(Compiler compiler) =>
-      implementsInterface(compiler.backend.jsIndexableClass, compiler);
-  bool isMutableIndexable(Compiler compiler) =>
-      implementsInterface(compiler.backend.jsMutableIndexableClass, compiler);
+  bool isIndexable(Compiler compiler) {
+    JavaScriptBackend backend = compiler.backend;
+    return implementsInterface(backend.jsIndexableClass, compiler);
+  }
+
+  bool isMutableIndexable(Compiler compiler) {
+    JavaScriptBackend backend = compiler.backend;
+    return implementsInterface(backend.jsMutableIndexableClass, compiler);
+  }
 
   bool implementsInterface(ClassElement interfaceElement, Compiler compiler) {
     DartType interfaceType = interfaceElement.computeType(compiler);