Merge CoreTypes and CoreClasses into CommonElements.

pkg/compiler/lib/src/resolution/signatures.dart

Index: pkg/compiler/lib/src/resolution/signatures.dart
diff --git a/pkg/compiler/lib/src/resolution/signatures.dart b/pkg/compiler/lib/src/resolution/signatures.dart
index faa927c43055f20dd33d9b8b67e191d6fc741392..0dd1363ba46d8a364c3d8b46da3346f74522ad2b 100644
--- a/pkg/compiler/lib/src/resolution/signatures.dart
+++ b/pkg/compiler/lib/src/resolution/signatures.dart
@@ -389,13 +389,13 @@ class SignatureResolver extends MappingVisitor<FormalElementX> {
           returnType = visitor.resolveReturnType(returnNode);
           break;
         case AsyncMarker.SYNC_STAR:
-          returnType = resolution.coreTypes.iterableType();
+          returnType = resolution.commonElements.iterableType();
           break;
         case AsyncMarker.ASYNC:
-          returnType = resolution.coreTypes.futureType();
+          returnType = resolution.commonElements.futureType();
           break;
         case AsyncMarker.ASYNC_STAR:
-          returnType = resolution.coreTypes.streamType();
+          returnType = resolution.commonElements.streamType();
           break;
       }
     }