[unittest] Fix out of memory error

This CL resets the TraceLoader caches after each describe that was
attached on the global scope this usally means one reset per file
but if you have describe('A'); describe('B'); on the top level of
one file it will rest 2 times.

Because we were never clearing this at one point we ended up with over 3GB on the heap.

Bug: none
Change-Id: I267faf321c0ad136f194db26bcca3ef08469464d
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6917688
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>
Commit-Queue: Nikolay Vitkov <nvitkov@chromium.org>

Author: Lightning00Blade

front_end/testing/TraceLoader.ts

@@ -284,6 +284,15 @@ export class TraceLoader {
     const traceContents = JSON.parse(contents) as Trace.Types.File.TraceFile;
     return traceContents;
   }
+
+  /**
+   * Karma test run in a single context if we load all the traces
+   * we risk getting out of memory
+   */
+  static resetCache() {
+    fileContentsCache.clear();
+    traceEngineCache.clear();
+  }
 }
 
 export async function fetchFileAsText(url: URL): Promise<string> {

front_end/testing/test_setup.ts

@@ -17,6 +17,7 @@ import * as ThemeSupport from '../ui/legacy/theme_support/theme_support.js';
 
 import {cleanTestDOM, raf, setupTestDOM} from './DOMHelpers.js';
 import {createFakeSetting, resetHostConfig} from './EnvironmentHelpers.js';
+import {TraceLoader} from './TraceLoader.js';
 import {
   checkForPendingActivity,
   startTrackingAsyncActivity,
@@ -32,7 +33,7 @@ document.documentElement.classList.add('platform-screenshot-test');
 const documentBodyElements = new Set<Element>();
 
 // Warm-up fonts to be readily available.
-before(async () => {
+before(async function() {
   const div = document.createElement('div');
   div.style.fontFamily = 'roboto';
   // Some latin characters to trigger the latin font file to be loaded.
@@ -42,6 +43,15 @@ before(async () => {
   document.body.append(div);
   await document.fonts.ready;
   div.remove();
+
+  // There is no way to provide after each file run via a test set up file.
+  // What we do instead is add and after all in all global test suits
+  // This is as close as we can get to after each file.
+  this.test?.parent?.suites.forEach(function(suite) {
+    suite.afterAll(function() {
+      TraceLoader.resetCache();
+    });
+  });
 });
 
 beforeEach(async () => {