Add basic memory profiling script to dev/ folder. (#238)

Add basic memory profiling script to `dev/` folder.

Author: Robert Jackson

.gitignore

@@ -3,3 +3,4 @@
 npm-debug.log
 tmp*
 dist/
+/snapshots

dev/memory-usage.js

@@ -0,0 +1,80 @@
+'use strict';
+
+/**
+ * This script is used for gathering basic memory statistics. It takes a heapsnapshot at the following locations:
+ *
+ * - `new FastBoot({ distPath: '...' })` - Saved in `snapshots/0-setup.heapsnapshot`
+ * - `await fastboot.visit('/')` - Saved in `snapshots/1-first-visit.heapsnapshot`
+ * - `await fastboot.visit('/')` - Saved in `snapshots/2-second-visit.heapsnapshot`
+ * - `await fastboot.visit('/')` - Saved in `snapshots/3-third-visit.heapsnapshot`
+ *
+ * General usage and evaluation steps:
+ *
+ * 1. run the script (e.g. `node dev/memory-usage.js`)
+ * 2. Navigate Chrome to the `about:blank`
+ * 3. Open the Chrome DevTools
+ * 4. Click into the "Memory" tab.
+ * 5. Click "Load" and load each of the files above (in order)
+ * 6. Review / evaluate
+ */
+
+const inspector = require('inspector');
+const path = require('path');
+const fs = require('fs');
+const session = new inspector.Session();
+
+session.connect();
+
+let file;
+// uses whatever the "current" file is
+session.on('HeapProfiler.addHeapSnapshotChunk', m => {
+  fs.writeSync(file, m.params.chunk);
+});
+
+function takeHeapSnapshot(path) {
+  file = fs.openSync(path, 'w');
+
+  return new Promise((resolve, reject) => {
+    session.post('HeapProfiler.takeHeapSnapshot', null, (err, r) => {
+      fs.closeSync(file);
+
+      if (err) {
+        reject(err);
+      }
+
+      resolve(r);
+    });
+  });
+}
+
+async function main() {
+  fs.mkdirSync('snapshots');
+
+  const FastBoot = require('../src/index');
+
+  const distPath = path.join(__dirname, '../test/fixtures/basic-app');
+  const fastboot = new FastBoot({
+    distPath,
+  });
+
+  await takeHeapSnapshot('snapshots/0-setup.heapsnapshot');
+
+  let result = await fastboot.visit('/');
+  await result.html();
+
+  await takeHeapSnapshot('snapshots/1-first-visit.heapsnapshot');
+
+  result = await fastboot.visit('/');
+  await result.html();
+
+  await takeHeapSnapshot('snapshots/2-second-visit.heapsnapshot');
+
+  result = await fastboot.visit('/');
+  await result.html();
+
+  await takeHeapSnapshot('snapshots/3-third-visit.heapsnapshot');
+}
+
+main().finally(() => {
+  session.disconnect();
+});