Use Chrome Headless instead of Electron

Since Chrome added an officially supported headless mode, there's no
reason to use Electron for our unit tests.  This will be both more accurate
(uses actual Chrome) and also gets rid of the rather large Electron
dependency.

WebGL is disabled in headless, so we only use headless on CI (because we
also disable webGL tests there).  When running locally, it just shows an
actual Chrome window. Chrome has an issue and plans to address this:
https://bugs.chromium.org/p/chromium/issues/detail?id=765284

.travis.yml

@@ -2,6 +2,8 @@ language: node_js
 node_js:
   - "8"
 sudo: false
+addons:
+  chrome: stable
 before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
@@ -17,7 +19,7 @@ script:
 
   - echo 'test webgl-stub' && echo -en 'travis_fold:start:script.test\\r'
   - npm run build
-  - npm run test -- --browsers Electron --webgl-stub --failTaskOnError --suppressPassed
+  - npm run test -- --browsers ChromeCI --webgl-stub --failTaskOnError --suppressPassed
   - echo -en 'travis_fold:end:script.test\\r'
 
   - echo 'makeZipFile' && echo -en 'travis_fold:start:script.makeZipFile\\r'
@@ -36,7 +38,7 @@ script:
   - echo -en 'travis_fold:end:script.deploy\\r'
 
   - echo 'test webgl-stub release' && echo -en 'travis_fold:start:script test.release\\r'
-  - npm run test -- --browsers Electron --failTaskOnError --webgl-stub --release --suppressPassed
+  - npm run test -- --browsers ChromeCI --failTaskOnError --webgl-stub --release --suppressPassed
   - echo -en 'travis_fold:end:script test.release\\r'
 
   - echo 'test node' && echo -en 'travis_fold:start:script test.node\\r'

Specs/karma.conf.js

@@ -64,8 +64,14 @@ module.exports = function(config) {
         // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher
         browsers : ['Chrome'],
 
-        electronOpts : {
-            show : false
+        //In Travis, we need to run with the no-sandbox flag
+        customLaunchers: {
+            ChromeCI: {
+                base: 'ChromeHeadless',
+                flags: [
+                    '--no-sandbox'
+                ]
+            }
         },
 
         browserNoActivityTimeout : 30000,

package.json

@@ -39,7 +39,6 @@
     "cloc": "^2.3.3",
     "compressible": "^2.0.9",
     "compression": "^1.6.2",
-    "electron": "^1.6.1",
     "eslint": "^4.0.0",
     "eslint-plugin-html": "^4.0.2",
     "event-stream": "^3.3.4",
@@ -58,7 +57,6 @@
     "karma-chrome-launcher": "^2.0.0",
     "karma-detect-browsers": "^2.2.3",
     "karma-edge-launcher": "^0.4.2",
-    "karma-electron": "^5.1.1",
     "karma-firefox-launcher": "^1.0.0",
     "karma-ie-launcher": "^1.0.0",
     "karma-jasmine": "^1.1.0",