dart2js cps: Use more precise type inference for direct index access.

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index b637d3ea3bc9f1824f117a1e9dffcc6f316d7665..ec239d6add46e42be0be2a8c49e285182b64f123 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -332,6 +332,9 @@ class JavaScriptBackend extends Backend {
 
   ClassElement jsInvocationMirrorClass;
 
+  ClassElement typedArrayClass;
+  ClassElement typedArrayOfIntClass;
+
   /// If [true], the compiler will emit code that logs whenever a method is
   /// called. When TRACE_METHOD is 'console' this will be logged
   /// directly in the JavaScript console. When TRACE_METHOD is 'post' the
@@ -2155,6 +2158,9 @@ class JavaScriptBackend extends Backend {
         htmlLibraryIsLoaded = true;
       } else if (uri == PACKAGE_LOOKUP_MAP) {
         lookupMapAnalysis.init(library);
+      } else if (uri == Uris.dart__native_typed_data) {
+        typedArrayClass = findClass('NativeTypedArray');
+        typedArrayOfIntClass = findClass('NativeTypedArrayOfInt');
       }
       annotations.onLibraryScanned(library);
     });