Alternative fix for the js-interop crash.

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index 9dde5bf1d0e501fc4010e3abe39ff206219c3a16..ae06d458c7279f3e6474ec51b2536e51a260dc48 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -79,6 +79,7 @@ class MockCompiler extends Compiler {
        // affected by inlining support.
        bool disableInlining: true,
        bool trustTypeAnnotations: false,
+       bool trustJSInteropTypeAnnotations: false,
        bool enableAsyncAwait: false,
        int this.expectedWarnings,
        int this.expectedErrors,
@@ -98,6 +99,7 @@ class MockCompiler extends Compiler {
               emitJavaScript: emitJavaScript,
               preserveComments: preserveComments,
               trustTypeAnnotations: trustTypeAnnotations,
+              trustJSInteropTypeAnnotations: trustJSInteropTypeAnnotations,
               diagnosticOptions:
                   new DiagnosticOptions(showPackageWarnings: true),
               outputProvider: new LegacyCompilerOutput(outputProvider)) {