Add tests for code cache fetch logic in ResourceLoader

Add tests for the defering logic in the code cache fetch.

Bug: chromium:812168, chromium:879494
Change-Id: Iac88631b4b5df3d13e327f2642f45fb285d2659f
Reviewed-on: https://chromium-review.googlesource.com/c/1209484
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604216}

third_party/blink/renderer/platform/loader/BUILD.gn

@@ -120,6 +120,7 @@ jumbo_source_set("unit_tests") {
     "fetch/raw_resource_test.cc",
     "fetch/resource_fetcher_test.cc",
     "fetch/resource_load_scheduler_test.cc",
+    "fetch/resource_loader_defer_loading_test.cc",
     "fetch/resource_loader_test.cc",
     "fetch/resource_request_test.cc",
     "fetch/resource_response_test.cc",