tests: run BrowserStack in parallel with Sauce Labs

Per https://github.com/twbs/bootstrap/issues/11087#issuecomment-31922999
and internal twbs team discussion.
Effectively reverts the deletions from #11701.

.travis.yml

@@ -20,9 +20,12 @@ env:
     - secure: "gqjqISbxBJK6byFbsmr1AyP1qoWH+rap06A2gI7v72+Tn2PU2nYkIMUkCvhZw6K889jv+LhQ/ybcBxDOXHpNCExCnSgB4dcnmYp+9oeNZb37jSP0rQ+Ib4OTLjzc3/FawE/fUq5kukZTC7porzc/k0qJNLAZRx3YLALmK1GIdUY="
     - secure: "Gghh/e3Gsbj1+4RR9Lh2aR/xJl35HWiHqlPIeSUqE9D7uDCVTAwNce/dGL3Ew7uJPfJ6Pgr70wD3zgu3stw0Zmzayax0hiDtGwcQCxVIER08wqGANK9C2Q7PYJkNTNtiTo6ehKWbdV4Z+/U+TEYyQfpQTDbAFYk/vVpsdjp0Lmc="
     - secure: "RTbRdx4G/2OTLfrZtP1VbRljxEmd6A1F3GqXboeQTldsnAlwpsES65es5CE3ub/rmixLApOY9ot7OPmNixFgC2Y8xOsV7lNCC62QVpmqQEDyGFFQKb3yO6/dmwQxdsCqGfzf9Np6Wh5V22QFvr50ZLKLd7Uhd9oXMDIk/z1MJ3o="
+    - secure: "Besg41eyU+2mfxrywQ4ydOShMdc34ImaO0S0ENP+aCOBuyNBIgP59wy5tBMmyai2/8eInYeVps4Td96mWInMMxzTe3Bar7eTLG5tWVKRSr/wc4NBPZ/ppoPAmCEsz9Y+VptRH9/FO8n7hsL9EFZ+xBKbG+C0SccGoyBDpA5j7/w="
+    - secure: "Ptiv7phCImFP3ALIz+sMQzrZg8k7C1gLZbFBhWxjnQr3g06wIfX3Ls5y9OHvxid+lOZZjISui3wzBVgpVHqwHUYf96+r0mo6/mJ+F4ffUmShZANVaIMD/JRTnXhUQJbvntGLvxn1EYWPdNM+2IHJrMipnjHxU9tkgAnlel4Zdew="
   matrix:
     - TWBS_TEST=core
     - TWBS_TEST=validate-html
     - TWBS_TEST=sauce-js-unit
+    - TWBS_TEST=browserstack-js-unit
 matrix:
   fast_finish: true

Gruntfile.js

@@ -351,6 +351,7 @@ module.exports = function (grunt) {
 
   // These plugins provide necessary tasks.
   require('load-grunt-tasks')(grunt, {scope: 'devDependencies'});
+  grunt.loadNpmTasks('browserstack-runner');
 
   // Docs HTML validation task
   grunt.registerTask('validate-html', ['jekyll', 'validation']);
@@ -372,6 +373,12 @@ module.exports = function (grunt) {
     testSubtasks.push('connect');
     testSubtasks.push('saucelabs-qunit');
   }
+  // Only run BrowserStack tests if there's a BrowserStack access key
+  if (typeof process.env.BROWSERSTACK_KEY !== 'undefined'
+      // Skip BrowserStack if running a different subset of the test suite
+      && (!process.env.TWBS_TEST || process.env.TWBS_TEST === 'browserstack-js-unit')) {
+    testSubtasks.push('browserstack_runner');
+  }
   grunt.registerTask('test', testSubtasks);
 
   // JS distribution task.

browserstack.json

+{
+  "username": "--secure--",
+  "key": "--secure--",
+  "test_path": "js/tests/index.html",
+  "browsers": [
+    {
+      "browser": "firefox",
+      "browser_version": "latest",
+      "os": "OS X",
+      "os_version": "Mavericks"
+    },
+    {
+      "browser": "safari",
+      "browser_version": "latest",
+      "os": "OS X",
+      "os_version": "Mavericks"
+    },
+    {
+      "browser": "chrome",
+      "browser_version": "latest",
+      "os": "OS X",
+      "os_version": "Mavericks"
+    },
+    {
+      "browser": "firefox",
+      "browser_version": "latest",
+      "os": "Windows",
+      "os_version": "8.1"
+    },
+    {
+      "browser": "chrome",
+      "browser_version": "latest",
+      "os": "Windows",
+      "os_version": "8.1"
+    },
+    {
+      "browser": "Mobile Safari",
+      "os": "ios",
+      "os_version": "7.0",
+      "device": "iPhone 5S"
+    }
+  ]
+}

package.json

@@ -25,6 +25,7 @@
     }
   ],
   "devDependencies": {
+    "browserstack-runner": "~0.0.13",
     "btoa": "~1.1.1",
     "grunt": "~0.4.2",
     "grunt-banner": "~0.2.0",