Introduce DartType.unaliased to avoid use of Resolution in the backend.

pkg/compiler/lib/src/typechecker.dart

Index: pkg/compiler/lib/src/typechecker.dart
diff --git a/pkg/compiler/lib/src/typechecker.dart b/pkg/compiler/lib/src/typechecker.dart
index fe017effa61383c5b570091cac3de6260f1d02fd..53eb6bad375370f54724a34eee0638af38c4cfe5 100644
--- a/pkg/compiler/lib/src/typechecker.dart
+++ b/pkg/compiler/lib/src/typechecker.dart
@@ -59,7 +59,6 @@ import 'tree/tree.dart';
 import 'util/util.dart' show
     Link,
     LinkBuilder;
-import '../compiler_new.dart' as api;
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
@@ -775,12 +774,12 @@ class TypeCheckerVisitor extends Visitor<DartType> {
     }
 
     DartType unaliasedBound =
-        Types.computeUnaliasedBound(compiler, receiverType);
+        Types.computeUnaliasedBound(resolution, receiverType);
     if (unaliasedBound.treatAsDynamic) {
       return new DynamicAccess();
     }
     InterfaceType interface =
-        Types.computeInterfaceType(compiler, unaliasedBound);
+        Types.computeInterfaceType(resolution, unaliasedBound);
     ElementAccess access = getAccess(memberName, unaliasedBound, interface);
     if (access != null) {
       return access;
@@ -793,10 +792,10 @@ class TypeCheckerVisitor extends Visitor<DartType> {
           TypePromotion typePromotion = typePromotions.head;
           if (!typePromotion.isValid) {
             DartType unaliasedBound =
-                Types.computeUnaliasedBound(compiler, typePromotion.type);
+                Types.computeUnaliasedBound(resolution, typePromotion.type);
             if (!unaliasedBound.treatAsDynamic) {
               InterfaceType interface =
-                  Types.computeInterfaceType(compiler, unaliasedBound);
+                  Types.computeInterfaceType(resolution, unaliasedBound);
               if (getAccess(memberName, unaliasedBound, interface) != null) {
                 reportTypePromotionHint(typePromotion);
               }
@@ -891,7 +890,8 @@ class TypeCheckerVisitor extends Visitor<DartType> {
   void analyzeArguments(Send send, Element element, DartType type,
                         [LinkBuilder<DartType> argumentTypes]) {
     Link<Node> arguments = send.arguments;
-    DartType unaliasedType = type.unalias(resolution);
+    type.computeUnaliased(resolution);
+    DartType unaliasedType = type.unaliased;
     if (identical(unaliasedType.kind, TypeKind.FUNCTION)) {
 
       /// Report [warning] including info(s) about the declaration of [element]
@@ -1013,8 +1013,9 @@ class TypeCheckerVisitor extends Visitor<DartType> {
       analyzeArguments(node, elementAccess.element, const DynamicType(),
                        argumentTypes);
     }
-    type = type.unalias(resolution);
-    if (identical(type.kind, TypeKind.FUNCTION)) {
+    type.computeUnaliased(resolution);
+    type = type.unaliased;
+    if (type.isFunctionType) {
       FunctionType funType = type;
       return funType.returnType;
     } else {
@@ -1151,7 +1152,7 @@ class TypeCheckerVisitor extends Visitor<DartType> {
       // Compute `B<double, dynamic>` as the subtype of `A<double, int>` using
       // the relation between `A<S, int>` and `A<double, int>`.
       MoreSpecificSubtypeVisitor visitor =
-          new MoreSpecificSubtypeVisitor(compiler);
+          new MoreSpecificSubtypeVisitor(types);
       InterfaceType shownTypeGeneric = visitor.computeMoreSpecific(
           shownClass, knownInterfaceType);
 
@@ -1845,7 +1846,7 @@ class TypeCheckerVisitor extends Visitor<DartType> {
           isHint: true);
     } else {
       InterfaceType interfaceType =
-          Types.computeInterfaceType(compiler, expressionType);
+          Types.computeInterfaceType(resolution, expressionType);
       if (interfaceType != null) {
         InterfaceType streamType =
             interfaceType.asInstanceOf(compiler.streamClass);