Merge pull request #9575 from atom/as-fix-bad-styling-on-scrollbars

Set initialLoadComplete to true only in test mode

src/atom-environment.coffee

@@ -117,7 +117,7 @@ class AtomEnvironment extends Model
 
   # Call .loadOrCreate instead
   constructor: (params={}) ->
-    {@blobStore, @applicationDelegate, @window, @document, configDirPath, @enablePersistence} = params
+    {@blobStore, @applicationDelegate, @window, @document, configDirPath, @enablePersistence, onlyLoadBaseStyleSheets} = params
 
     @state = {version: @constructor.version}
 
@@ -183,7 +183,7 @@ class AtomEnvironment extends Model
 
     @themes.loadBaseStylesheets()
     @initialStyleElements = @styles.getSnapshot()
-    @themes.initialLoadComplete = true
+    @themes.initialLoadComplete = true if onlyLoadBaseStyleSheets
     @setBodyPlatformClass()
 
     @stylesElement = @styles.buildStylesElement()

src/initialize-test-window.coffee

@@ -70,6 +70,7 @@ module.exports = ({blobStore}) ->
     buildAtomEnvironment = (params) ->
       params = cloneObject(params)
       params.blobStore = blobStore unless params.hasOwnProperty("blobStore")
+      params.onlyLoadBaseStyleSheets = true unless params.hasOwnProperty("onlyLoadBaseStyleSheets")
       new AtomEnvironment(params)
 
     promise = testRunner({