Break out window.applyStylesheet from window.requireStylesheet

This will be useful in applying generated stylesheets associated with themes.

spec/app/window-spec.coffee

@@ -32,15 +32,15 @@ describe "Window", ->
 
   describe "requireStylesheet(path)", ->
     it "synchronously loads the stylesheet at the given path and installs a style tag for it in the head", ->
-      $('head style[path*="atom.css"]').remove()
+      $('head style[id*="atom.css"]').remove()
       lengthBefore = $('head style').length
       requireStylesheet('atom.css')
       expect($('head style').length).toBe lengthBefore + 1
 
-      styleElt = $('head style[path*="atom.css"]')
+      styleElt = $('head style[id*="atom.css"]')
 
       fullPath = require.resolve('atom.css')
-      expect(styleElt.attr('path')).toBe fullPath
+      expect(styleElt.attr('id')).toBe fullPath
       expect(styleElt.text()).toBe fs.read(fullPath)
 
       # doesn't append twice

src/app/window.coffee

@@ -53,9 +53,11 @@ windowAdditions =
 
   requireStylesheet: (path) ->
     fullPath = require.resolve(path)
-    content = fs.read(fullPath)
-    return if $("head style[path='#{fullPath}']").length
-    $('head').append "<style path='#{fullPath}'>#{content}</style>"
+    window.applyStylesheet(fullPath, fs.read(fullPath))
+
+  applyStylesheet: (id, text) ->
+    unless $("head style[id='#{id}']").length
+      $('head').append "<style id='#{id}'>#{text}</style>"
 
   requireExtension: (name) ->
     extensionPath = require.resolve name