GVN getInterceptor and use the interceptor constant when the type is known.

sdk/lib/_internal/compiler/implementation/lib/interceptors.dart

Index: sdk/lib/_internal/compiler/implementation/lib/interceptors.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/lib/interceptors.dart	(revision 15265)
+++ sdk/lib/_internal/compiler/implementation/lib/interceptors.dart	(working copy)
@@ -24,16 +24,28 @@
  * defined in an interceptor class.
  */
 getInterceptor(object) {
-  if (object is String) return const JSString();
-  if (isJsArray(object)) return const JSArray();
-  if (object is int) return const JSInt();
-  if (object is double) return const JSDouble();
-  if (object is bool) return const JSBool();
-  if (object == null) return const JSNull();
-  if (JS('String', 'typeof #', object) == 'function') return const JSFunction();
-  return const ObjectInterceptor();
+  if (object is String) return stringInterceptor;
+  if (isJsArray(object)) return arrayInterceptor;
+  if (object is int) return intInterceptor;
+  if (object is double) return doubleInterceptor;
+  if (object is bool) return boolInterceptor;
+  if (object == null) return nullInterceptor;
+  if (JS('String', 'typeof #', object) == 'function') {
+    return functionInterceptor;
+  }
+  return objectInterceptor;
 }
 
+final arrayInterceptor = const JSArray();
+final boolInterceptor = const JSBool();
+final doubleInterceptor = const JSDouble();
+final intInterceptor = const JSInt();
+final functionInterceptor = const JSFunction();
+final nullInterceptor = const JSNull();
+final numberInterceptor = const JSNumber();
+final stringInterceptor = const JSString();
+final objectInterceptor = const ObjectInterceptor();
+
 /**
  * The interceptor class for tear-off static methods. Unlike
  * tear-off instance methods, tear-off static methods are just the JS