fix(karma): set defaults for karma.conf.js (#1837)

The karma plugin is currently overwriting configuration set in karma.conf.js instead of merging existing values. This fix will set defaults but not overwrite existing configuration.

packages/angular-cli/plugins/karma.js

@@ -12,8 +12,8 @@ const init = (config) => {
   const environment = config.angularCli.environment || 'dev';
 
   // add webpack config
-  config.webpack = getWebpackTestConfig(config.basePath, environment, appConfig);
-  config.webpackMiddleware = {
+  const webpackConfig = getWebpackTestConfig(config.basePath, environment, appConfig);
+  const webpackMiddlewareConfig = {
     noInfo: true, // Hide webpack output because its noisy.
     stats: { // Also prevent chunk and module display output, cleaner look. Only emit errors.
       assets: false,
@@ -25,6 +25,8 @@ const init = (config) => {
       chunkModules: false
     }
   };
+  config.webpack = Object.assign(webpackConfig, config.webpack);
+  config.webpackMiddleware = Object.assign(webpackMiddlewareConfig, config.webpackMiddleware);
 
   // replace the angular-cli preprocessor with webpack+sourcemap
   Object.keys(config.preprocessors)