Ensure the type inferrer does not infer types for runtime helpers used by the backend.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 204 matching lines @@
   /// Called by [MirrorUsageAnalyzerTask] after it has merged all @MirrorsUsed
   /// annotations. The arguments corresponds to the unions of the corresponding
   /// fields of the annotations.
   void registerMirrorUsage(Set<String> symbols,
                            Set<Element> targets,
                            Set<Element> metaTargets) {}
 
   /// Returns true if this element should be retained for reflection even if it
   /// would normally be tree-shaken away.
   bool isNeededForReflection(Element element) => false;
+
+  /// Returns true if global optimizations such as type inferencing
+  /// can apply to this element. One category of elements that do not
+  /// apply is runtime helpers that the backend calls, but the
+  /// optimizations don't see those calls.
+  bool canBeUsedForGlobalOptimizations(Element element);
 }
 
 /**
  * Key class used in [TokenMap] in which the hash code for a token is based
  * on the [charOffset].
  */
 class TokenKey {
   final Token token;
   TokenKey(this.token);
   int get hashCode => token.charOffset;
@@ skipping 1245 matching lines @@
 
   void close() {}
 
   toString() => name;
 
   /// Convenience method for getting an [api.CompilerOutputProvider].
   static NullSink outputProvider(String name, String extension) {
     return new NullSink('$name.$extension');
   }
 }