Support [AssumeDynamic] and [TrustTypeAnnotations] in the inferrer.

pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart

Index: pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
diff --git a/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart b/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
index f60b4c583d09fe561fb5874fc12c3cc087c31579..730466152cc209303d720755402bb4ed002ab1c8 100644
--- a/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
+++ b/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
@@ -45,6 +45,7 @@ import '../util/util.dart'
     show ImmutableEmptySet,
          Setlet,
          Spannable;
+import '../js_backend/js_backend.dart' show Annotations, JavaScriptBackend;
 
 import 'inferrer_visitor.dart'
     show ArgumentsTypes,
@@ -559,6 +560,9 @@ class TypeGraphInferrerEngine
   TypeGraphInferrerEngine(Compiler compiler, this.mainElement)
         : super(compiler, new TypeInformationSystem(compiler));
 
+  JavaScriptBackend get backend => compiler.backend;
+  Annotations get annotations => backend.annotations;
+
   /**
    * A set of selector names that [List] implements, that we know return
    * their element type.