Add a new flag to dart2js: --trust-type-annotations and implement it in the types inferrer.

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 233 matching lines @@
    * correspond to a particular element.
    *
    * We should get rid of this and ensure that all dependencies are
    * associated with a particular element.
    */
   final TreeElements globalDependencies = new TreeElementMapping(null);
 
   final bool enableMinification;
   final bool enableTypeAssertions;
   final bool enableUserAssertions;
+  final bool trustTypeAnnotations;
   final bool enableConcreteTypeInference;
   /**
    * The maximum size of a concrete type before it widens to dynamic during
    * concrete type inference.
    */
   final int maxConcreteTypeSize;
   final bool analyzeAll;
   final bool analyzeOnly;
   /**
    * If true, skip analysis of method bodies and field initializers. Implies
@@ skipping 169 matching lines @@
   static const int PHASE_COMPILING = 3;
   int phase;
 
   bool compilationFailed = false;
 
   bool hasCrashed = false;
 
   Compiler({this.tracer: const Tracer(),
             this.enableTypeAssertions: false,
             this.enableUserAssertions: false,
+            this.trustTypeAnnotations: false,
             this.enableConcreteTypeInference: false,
             this.maxConcreteTypeSize: 5,
             this.enableMinification: false,
             this.enableNativeLiveTypeAnalysis: false,
             bool emitJavaScript: true,
             bool generateSourceMap: true,
             bool disallowUnsafeEval: false,
             this.analyzeAll: false,
             bool analyzeOnly: false,
             bool analyzeSignaturesOnly: false,
@@ skipping 872 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');
   }
 }