Fix type checks and display for JS interop types.

pkg/dev_compiler/karma.conf.js

Index: pkg/dev_compiler/karma.conf.js
diff --git a/pkg/dev_compiler/karma.conf.js b/pkg/dev_compiler/karma.conf.js
index e9041061fb0f3b83f1911b0800f6a7e1ee6f641c..06edd81742d20b67b60bf914b0d60615457b070c 100644
--- a/pkg/dev_compiler/karma.conf.js
+++ b/pkg/dev_compiler/karma.conf.js
@@ -18,6 +18,7 @@ module.exports = function(config) {
       {pattern: 'gen/codegen_output/language/**/*.js', included: false},
       {pattern: 'gen/codegen_output/corelib/**/*.js', included: false},
       {pattern: 'gen/codegen_output/lib/**/*.js', included: false},
+      {pattern: 'gen/codegen_tests/lib/**/*.txt', included: false},
       {pattern: 'test/browser/*.js', included: false},
       {pattern: 'node_modules/is_js/*.js', included: false},      
       'test-main.js',
@@ -47,6 +48,11 @@ module.exports = function(config) {
     // web server port
     port: 9876,
 
+    // Proxy required to serve resources needed by tests.
+    proxies: {
+      '/root_dart/tests/lib/': '/base/gen/codegen_tests/lib/'
+    },
+
     // enable / disable colors in the output (reporters and logs)
     colors: true,