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

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index a461a3a3478adb61c58c4c6233039df3eca12be0..fd597112c4f1b662fda27bf39d1d41587d3c4889 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -1111,9 +1111,6 @@ class SsaBuilder extends ast.Visitor
 
   DiagnosticReporter get reporter => compiler.reporter;
 
-  // TODO(johnniwinther): Avoid the need for this.
-  Resolution get resolution => compiler.resolution;
-
   @override
   SemanticSendVisitor get sendVisitor => this;
 
@@ -2488,7 +2485,7 @@ class SsaBuilder extends ast.Visitor
                                    DartType type,
                                    int kind) {
     if (type == null) return original;
-    type = type.unalias(resolution);
+    type = type.unaliased;
     assert(assertTypeInContext(type, original));
     if (type.isInterfaceType && !type.treatAsRaw) {
       TypeMask subtype = new TypeMask.subtype(type.element, compiler.world);
@@ -2524,7 +2521,7 @@ class SsaBuilder extends ast.Visitor
     assert(compiler.trustTypeAnnotations);
     assert(type != null);
     type = localsHandler.substInContext(type);
-    type = type.unalias(resolution);
+    type = type.unaliased;
     if (type.isDynamic) return original;
     if (!type.isInterfaceType) return original;
     // The type element is either a class or the void element.
@@ -3820,7 +3817,7 @@ class SsaBuilder extends ast.Visitor
   HInstruction buildIsNode(ast.Node node,
                            DartType type,
                            HInstruction expression) {
-    type = localsHandler.substInContext(type).unalias(resolution);
+    type = localsHandler.substInContext(type).unaliased;
     if (type.isFunctionType) {
       List arguments = [buildFunctionType(type), expression];
       pushInvokeDynamic(
@@ -8992,7 +8989,7 @@ class TypeBuilder implements DartTypeVisitor<dynamic, SsaBuilder> {
   }
 
   void visitTypedefType(TypedefType type, SsaBuilder builder) {
-    DartType unaliased = type.unalias(builder.compiler.resolution);
+    DartType unaliased = type.unaliased;
     if (unaliased is TypedefType) throw 'unable to unalias $type';
     unaliased.accept(this, builder);
   }