[DevTools] Updates Karma to report coverage

The Karma tests that run do not currently produce a coverage report.
This CL adds local coverage reporting with a view to start exposing the
reports at the CQ level eventually.

Change-Id: Id374ee34c911a5762ce37ad69799fe00bcf1c29d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1831760
Commit-Queue: Paul Lewis <aerotwist@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701116}

DEPS

@@ -238,7 +238,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling devtools-node-modules
   # and whatever else without interference from each other.
-  'devtools_node_modules_revision': '499e57bfea8a4f8e8373321f2c99632372553e56',
+  'devtools_node_modules_revision': '42d0028a8621347b04fa31462b33a32cd105d715',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling libprotobuf-mutator
   # and whatever else without interference from each other.

third_party/blink/renderer/devtools/.gitignore

@@ -19,8 +19,9 @@ npm-debug.log
 package-lock.json
 .vscode
 /front_end/*/jsconfig.json
+karma-coverage
 
 # These are generated for build and would be put in the symlinked folder (thus this folder)
 front_end/InspectorBackendCommands.js
 front_end/SupportedCSSProperties.js
-front_end/accessibility/ARIAProperties.js
\ No newline at end of file
+front_end/accessibility/ARIAProperties.js

third_party/blink/renderer/devtools/karma.conf.js

@@ -13,15 +13,13 @@ module.exports = function(config) {
     },{
       pattern: 'tests/**/*.ts',
       type: 'module'
-    }, {
-      pattern: 'tests/**/*.js',
-      type: 'module'
     }],
 
-    reporters: ["dots"],
+    reporters: ["dots", "coverage-istanbul"],
 
     preprocessors: {
-      './tests/**/*.ts': ['karma-typescript']
+      './tests/**/*.ts': ['karma-typescript'],
+      './front_end/common/*.js': ['karma-coverage-istanbul-instrumenter']
     },
 
     browsers: ["ChromeHeadless"],
@@ -55,9 +53,20 @@ module.exports = function(config) {
       "karma-chrome-launcher",
       "karma-mocha",
       "karma-chai",
-      "karma-typescript"
+      "karma-typescript",
+      require('../../../../third_party/devtools-node-modules/third_party/node_modules/karma-coverage-istanbul-instrumenter'),
+      require('../../../../third_party/devtools-node-modules/third_party/node_modules/karma-coverage-istanbul-reporter')
     ],
 
+    coverageIstanbulInstrumenter: {
+      esModules: true
+    },
+
+    coverageIstanbulReporter: {
+      reports: ["text", "html"],
+      dir: "karma-coverage"
+    },
+
     singleRun: true
   };