Disabling autoprefixer in css-loader, explicitly using postcss-loader (#9899)

When the UglifyJsPlugin is used for production, it's setting the minimize property for the loaders in the pipeline. This was causing the css-loader to call cssnano which was itself then calling autoprefixer.

We were explicitly calling autoprefixer via the postcss-loader for all style loaders that utilized a preprocessor and specifying the list of supported browsers, specifically to set the prefixes for PhantomJS. When the autoprefixer was run as part of the css-loader, the list of browsers wasn't present and this was causing the prefixes that we added to be removed.

This removes the implicit use of autoprefixer from the css-loader and instead explicitly uses the postcss-loader for all style loaders, passing in the proper configuration.

src/optimize/base_optimizer.js

@@ -71,18 +71,18 @@ class BaseOptimizer {
 
     const makeStyleLoader = preprocessor => {
       let loaders = [
-        loaderWithSourceMaps('css-loader')
+        loaderWithSourceMaps('css-loader?autoprefixer=false'),
+        {
+          name: 'postcss-loader',
+          query: {
+            config: require.resolve('./postcss.config')
+          }
+        },
       ];
 
       if (preprocessor) {
         loaders = [
           ...loaders,
-          {
-            name: 'postcss-loader',
-            query: {
-              config: require.resolve('./postcss.config')
-            }
-          },
           loaderWithSourceMaps(preprocessor)
         ];
       }