Wait for initial stylesheet load to complete

Instead of measuring on each stylesheet load at startup,
wait for the initial load of all the stylesheets to complete
and then do the necessary measurments.

src/editor-component.coffee

@@ -179,6 +179,8 @@ EditorComponent = React.createClass
     @subscribe atom.themes.onDidAddStylesheet @onStylesheetsChanged
     @subscribe atom.themes.onDidUpdateStylesheet @onStylesheetsChanged
     @subscribe atom.themes.onDidRemoveStylesheet @onStylesheetsChanged
+    unless atom.themes.isInitialLoadComplete()
+      @subscribe atom.themes.onDidReloadAll @onStylesheetsChanged
     @subscribe scrollbarStyle.changes, @refreshScrollbars
 
     @domPollingIntervalId = setInterval(@pollDOM, @domPollingInterval)
@@ -708,6 +710,7 @@ EditorComponent = React.createClass
 
   onStylesheetsChanged: (stylesheet) ->
     return unless @performedInitialMeasurement
+    return unless atom.themes.isInitialLoadComplete()
 
     @refreshScrollbars() if @containsScrollbarSelector(stylesheet)
     @sampleFontStyling()

src/theme-manager.coffee

@@ -20,6 +20,7 @@ class ThemeManager
   constructor: ({@packageManager, @resourcePath, @configDirPath, @safeMode}) ->
     @emitter = new Emitter
     @lessCache = null
+    @initialLoadComplete = false
     @packageManager.registerPackageActivator(this, ['theme'])
 
   ###
@@ -165,6 +166,7 @@ class ThemeManager
         @refreshLessCache() # Update cache again now that @getActiveThemes() is populated
         @loadUserStylesheet()
         @reloadBaseStylesheets()
+        @initialLoadComplete = true
         @emit 'reloaded'
         @emitter.emit 'did-reload-all'
         deferred.resolve()
@@ -177,6 +179,8 @@ class ThemeManager
     @packageManager.deactivatePackage(pack.name) for pack in @getActiveThemes()
     null
 
+  isInitialLoadComplete: -> @initialLoadComplete
+
   addActiveThemeClasses: ->
     for pack in @getActiveThemes()
       atom.workspaceView?[0]?.classList.add("theme-#{pack.name}")