use production or staging hosts for static assets url

.travis.yml

@@ -43,6 +43,11 @@ env:
   - PROJECT_HOST_VAR=PROJECT_HOST_$TRAVIS_BRANCH
   - PROJECT_HOST=${!PROJECT_HOST_VAR}
   - PROJECT_HOST=${PROJECT_HOST:-$PROJECT_HOST_STAGING}
+  - STATIC_HOST_master=https://cdn2.scratch.mit.edu
+  - STATIC_HOST_STAGING=https://scratch.ly
+  - STATIC_HOST_VAR=STATIC_HOST_$TRAVIS_BRANCH
+  - STATIC_HOST=${!STATIC_HOST_VAR}
+  - STATIC_HOST=${STATIC_HOST:-$STATIC_HOST_STAGING}
   - PATH=$PATH:$PWD/test/integration/node_modules/chromedriver/bin
   - AWS_ACCESS_KEY_ID=$EB_AWS_ACCESS_KEY_ID
   - AWS_SECRET_ACCESS_KEY=$EB_AWS_SECRET_ACCESS_KEY

src/lib/user-thumbnail.js

@@ -11,7 +11,8 @@
  * @returns {string} thumbnail url string
  */
 const thumbnailUrl = (userId, width, height) => (
-    `/get_image/user/${userId}_${width ? width : 32}x${height ? height : (width ? width : 32)}.png`
+    `${process.env.STATIC_HOST}/get_image/user/${userId}_` +
+        `${width ? width : 32}x${height ? height : (width ? width : 32)}.png`
 );
 
 module.exports = thumbnailUrl;

webpack.config.js

@@ -33,7 +33,7 @@ VersionPlugin.prototype.apply = function (compiler) {
         callback();
     };
     const options = this.options;
-    
+
     compiler.plugin('emit', function (compilation, callback) {
         const sha = process.env.WWW_VERSION;
         if (!sha) { // eslint-disable-line no-negated-condition
@@ -169,6 +169,7 @@ module.exports = {
                 'process.env.BACKPACK_HOST': '"' + (process.env.BACKPACK_HOST || 'https://backpack.scratch.mit.edu') + '"',
                 'process.env.CLOUDDATA_HOST': '"' + (process.env.CLOUDDATA_HOST || 'clouddata.scratch.mit.edu') + '"',
                 'process.env.PROJECT_HOST': '"' + (process.env.PROJECT_HOST || 'https://projects.scratch.mit.edu') + '"',
+                'process.env.STATIC_HOST': '"' + (process.env.STATIC_HOST || 'https://cdn2.scratch.mit.edu') + '"',
                 'process.env.SCRATCH_ENV': '"' + (process.env.SCRATCH_ENV || 'development') + '"'
             }),
             new webpack.optimize.CommonsChunkPlugin({