Create specialized versions of getInterceptor.

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 15381)
+++ sdk/lib/_internal/compiler/implementation/lib/interceptors.dart	(working copy)
@@ -23,29 +23,12 @@
  * to emit a call to an intercepted method, that is a method that is
  * defined in an interceptor class.
  */
-getInterceptor(object) {
-  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;
+getInterceptor() {
+  // This is a magic method: the compiler does specialization of it
+  // depending on the uses of intercepted methods and instantiated
+  // primitive types.
 }
 
-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