Support requiring stylesheets without an extension

Stylesheets will attempt to be resolved with both css
and less extensions if no extension is included in the
path specified to requireStylesheet().

spec/app/window-spec.coffee

@@ -94,7 +94,7 @@ describe "Window", ->
 
       $('head style[id*="css.css"]').remove()
 
-    it  "synchronously loads and parses less files at the given path and installs a style tag for it in the head", ->
+    it "synchronously loads and parses less files at the given path and installs a style tag for it in the head", ->
       lessPath = project.resolve('sample.less')
       lengthBefore = $('head style').length
       requireStylesheet(lessPath)
@@ -117,7 +117,16 @@ describe "Window", ->
       expect($('head style').length).toBe lengthBefore + 1
       $('head style[id*="sample.less"]').remove()
 
-  describe ".disableStyleSheet(path)", ->
+    it "supports requiring css and less stylesheets without an explicit extension", ->
+      requireStylesheet 'fixtures/css'
+      expect($('head style[id*="css.css"]').attr('id')).toBe project.resolve('css.css')
+      requireStylesheet 'fixtures/sample'
+      expect($('head style[id*="sample.less"]').attr('id')).toBe project.resolve('sample.less')
+
+      $('head style[id*="css.css"]').remove()
+      $('head style[id*="sample.less"]').remove()
+
+  describe ".removeStylesheet(path)", ->
     it "removes styling applied by given stylesheet path", ->
       cssPath = require.resolve(fs.join("fixtures", "css.css"))
 

src/app/window.coffee

@@ -24,14 +24,14 @@ window.setUpEnvironment = ->
   $(document).on 'keydown', keymap.handleKeyEvent
   keymap.bindDefaultKeys()
 
-  requireStylesheet 'reset.less'
-  requireStylesheet 'atom.less'
-  requireStylesheet 'overlay.less'
-  requireStylesheet 'popover-list.less'
-  requireStylesheet 'notification.less'
-  requireStylesheet 'markdown.less'
+  requireStylesheet 'reset'
+  requireStylesheet 'atom'
+  requireStylesheet 'overlay'
+  requireStylesheet 'popover-list'
+  requireStylesheet 'notification'
+  requireStylesheet 'markdown'
 
-  if nativeStylesheetPath = fs.resolveOnLoadPath("#{process.platform}.css")
+  if nativeStylesheetPath = fs.resolveOnLoadPath(process.platform, ['css', 'less'])
     requireStylesheet(nativeStylesheetPath)
 
 # This method is only called when opening a real application window
@@ -111,8 +111,14 @@ window.deserializeWindowState = ->
 window.stylesheetElementForId = (id) ->
   $("head style[id='#{id}']")
 
+window.resolveStylesheet = (path) ->
+  if fs.extension(path).length > 0
+    fs.resolveOnLoadPath(path)
+  else
+    fs.resolveOnLoadPath(path, ['css', 'less'])
+
 window.requireStylesheet = (path) ->
-  if fullPath = require.resolve(path)
+  if fullPath = window.resolveStylesheet(path)
     content = window.loadStylesheet(fullPath)
     window.applyStylesheet(fullPath, content)
   else
@@ -128,7 +134,7 @@ window.loadStylesheet = (path) ->
   content
 
 window.removeStylesheet = (path) ->
-  unless fullPath = require.resolve(path)
+  unless fullPath = window.resolveStylesheet(path)
     throw new Error("Could not find a file at path '#{path}'")
   window.stylesheetElementForId(fullPath).remove()
 

src/stdlib/fs-utils.coffee

@@ -218,6 +218,12 @@ module.exports =
     pathToResolve = args.pop()
     loadPaths = args
 
+    if pathToResolve[0] is '/'
+      if extensions and resolvedPath = @resolveExtension(pathToResolve, extensions)
+        return resolvedPath
+      else
+        return pathToResolve if @exists(pathToResolve)
+
     for loadPath in loadPaths
       candidatePath = @join(loadPath, pathToResolve)
       if extensions