Speedup build and CI testing (tensorflow#1624)

Speedup our travis CI build and testing by 2X.

This run took: 8 min 33 sec [link](https://travis-ci.org/tensorflow/tfjs-core/builds/506838185)
Yesterday's run took: 16min 53 sec [link](https://travis-ci.org/tensorflow/tfjs-core/builds/506570451)

**Details**
- We used to re-compile our codebase 10 times over (every time you call `ts-node` and `karma`)
- Now we compile it only once (`yarn build`) and run `node` and `karma` using the `browserify` plugin, which circumvents the typescript compilation
- Also speedup the vscode `build` task by 1.5X by passing `--noEmit` to typescript to skip generating build artifacts.

DEV

Author: dsmilkov

.vscode/tasks.json

@@ -18,7 +18,7 @@
         "command": "yarn",
         "label": "build",
         "type": "shell",
-        "args": ["build", "--pretty", "false"],
+        "args": ["build", "--pretty", "false", "--noEmit"],
         "problemMatcher": [
           "$tsc"
         ]

karma.conf.js

@@ -31,6 +31,26 @@ if (coverageEnabled) {
   karmaTypescriptConfig.reports = {html: 'coverage', 'text-summary': ''};
 }
 
+const devConfig = {
+  frameworks: ['jasmine', 'karma-typescript'],
+  files: [{pattern: 'src/**/*.ts'}],
+  exclude: ['src/test_node.ts'],
+  preprocessors: {'**/*.ts': ['karma-typescript']},
+  karmaTypescriptConfig,
+  reporters: ['dots', 'karma-typescript'],
+};
+
+const browserstackConfig = {
+  frameworks: ['browserify', 'jasmine'],
+  files: [{pattern: 'dist/**/*_test.js'}],
+  exclude: ['dist/test_node.js'],
+  preprocessors: {'dist/**/*_test.js': ['browserify']},
+  browserify: {debug: false},
+  reporters: ['dots', 'BrowserStack'],
+  singleRun: true,
+  hostname: 'bs-local.com',
+};
+
 module.exports = function(config) {
   const args = [];
   if (config.backend) {
@@ -42,14 +62,10 @@ module.exports = function(config) {
   if (config.features) {
     args.push('--features', config.features);
   }
+  const extraConfig = config.browserstack ? browserstackConfig : devConfig;
 
   config.set({
-    frameworks: ['jasmine', 'karma-typescript'],
-    files: [{pattern: 'src/**/*.ts'}],
-    exclude: ['src/test_node.ts'],
-    preprocessors: {'**/*.ts': ['karma-typescript']},
-    karmaTypescriptConfig,
-    reporters: ['dots', 'karma-typescript'],
+    ...extraConfig,
     browsers: ['Chrome'],
     browserStack: {
       username: process.env.BROWSERSTACK_USERNAME,
@@ -59,6 +75,8 @@ module.exports = function(config) {
     reportSlowerThan: 500,
     browserNoActivityTimeout: 180000,
     customLaunchers: {
+      // For browserstack configs see:
+      // https://www.browserstack.com/automate/node
       bs_chrome_mac: {
         base: 'BrowserStack',
         browser: 'chrome',

package.json

@@ -20,10 +20,12 @@
   "devDependencies": {
     "@types/jasmine": "~2.5.53",
     "@types/node": "~9.6.0",
+    "browserify": "~16.2.3",
     "clang-format": "~1.2.4",
     "jasmine": "~3.1.0",
     "jasmine-core": "~3.1.0",
     "karma": "~4.0.0",
+    "karma-browserify": "~6.0.0",
     "karma-browserstack-launcher": "~1.4.0",
     "karma-chrome-launcher": "~2.2.0",
     "karma-jasmine": "~1.1.0",
@@ -49,9 +51,9 @@
     "lint": "tslint -p . -t verbose",
     "coverage": "KARMA_COVERAGE=1 karma start --browsers='Chrome' --singleRun",
     "test": "karma start",
-    "run-browserstack": "karma start --singleRun --reporters='dots,karma-typescript,BrowserStack' --hostname='bs-local.com'",
+    "run-browserstack": "karma start --browserstack",
     "test-benchmark": "cd integration_tests/benchmarks && yarn benchmark-travis && cd ../../",
-    "test-node": "ts-node src/test_node.ts",
+    "test-node": "node dist/test_node.js",
     "test-integration": "./scripts/test-integration.sh",
     "test-travis": "./scripts/test-travis.sh"
   },

scripts/build-npm.sh

@@ -22,4 +22,3 @@ yarn
 yarn build
 rollup -c
 echo "Stored standalone library at dist/tf-core(.min).js"
-npm pack

src/test_node.ts

@@ -28,5 +28,5 @@ setTestEnvs(
     [{name: 'node', factory: () => new MathBackendCPU(), features: {}}]);
 
 const runner = new jasmine();
-runner.loadConfig({spec_files: ['src/**/**_test.ts'], random: false});
+runner.loadConfig({spec_files: ['dist/**/**_test.js'], random: false});
 runner.execute();