Enable PerformanceManager in WebTestContentRendererClient

The performance.measureMemory API relies on PerformanceManager, so we
need to enable PerformanceManager to run web platform tests.

Bug: 1085129
Change-Id: I5e49a35025928526d8e5a36a07e8dcecf2793977
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551122Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830999}

content/web_test/renderer/web_test_content_renderer_client.cc

@@ -134,6 +134,8 @@ void WebTestContentRendererClient::DidInitializeWorkerContextOnWorkerThread(
 
 void WebTestContentRendererClient::
     SetRuntimeFeaturesDefaultsBeforeBlinkInitialization() {
+  // PerformanceManager is used by measure-memory web platform tests.
+  blink::WebRuntimeFeatures::EnablePerformanceManagerInstrumentation(true);
   // We always expose GC to web tests.
   std::string flags("--expose-gc");
   auto* command_line = base::CommandLine::ForCurrentProcess();