Add a warning whenever link preloads are not used

third_party/WebKit/Source/core/fetch/ResourceFetcherTest.cpp

 /*
  * Copyright (c) 2013, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 586 matching lines @@
     response.setHTTPStatusCode(200);
     URLTestHelpers::registerMockedURLLoadWithCustomResponse(url, testImageFilename, WebString::fromUTF8(""), WrappedResourceResponse(response));
 
     FetchRequest fetchRequestOriginal = FetchRequest(url, FetchInitiatorInfo());
     fetchRequestOriginal.setLinkPreload(true);
     Resource* resource = fetcher->requestResource(fetchRequestOriginal, TestResourceFactory(Resource::Image));
     ASSERT_TRUE(resource);
     EXPECT_TRUE(resource->isLinkPreload());
     Platform::current()->getURLLoaderMockFactory()->serveAsynchronousRequests();
     fetcher->preloadStarted(resource);
+    EXPECT_TRUE(fetcher->hasUnusedLinkPreloads());
 
     FetchRequest fetchRequestSecond = FetchRequest(url, FetchInitiatorInfo());
     fetchRequestSecond.setLinkPreload(true);
     Resource* secondResource = fetcher2->requestResource(fetchRequestSecond, TestResourceFactory(Resource::Image));
     ASSERT_TRUE(secondResource);
     EXPECT_TRUE(secondResource->isLinkPreload());
     Platform::current()->getURLLoaderMockFactory()->serveAsynchronousRequests();
     fetcher2->preloadStarted(secondResource);
+    EXPECT_TRUE(fetcher2->hasUnusedLinkPreloads());
+
+    // Link rel preload scanner
+    FetchRequest fetchRequestLinkPreloadScanner = FetchRequest(url, FetchInitiatorInfo());
+    fetchRequestLinkPreloadScanner.setLinkPreload(true);
+    Resource* linkPreloadScannerResource = fetcher->requestResource(fetchRequestLinkPreloadScanner, TestResourceFactory(Resource::Image));
+    EXPECT_EQ(resource, linkPreloadScannerResource);
+    EXPECT_TRUE(resource->isLinkPreload());
+    fetcher->preloadStarted(resource);
+    EXPECT_TRUE(fetcher->hasUnusedLinkPreloads());
+    EXPECT_TRUE(fetcher2->hasUnusedLinkPreloads());
 
     // Image preload scanner
     FetchRequest fetchRequestPreloadScanner = FetchRequest(url, FetchInitiatorInfo());
     Resource* imgPreloadScannerResource = fetcher->requestResource(fetchRequestPreloadScanner, TestResourceFactory(Resource::Image));
     EXPECT_EQ(resource, imgPreloadScannerResource);
     EXPECT_FALSE(resource->isLinkPreload());
     fetcher->preloadStarted(resource);
+    EXPECT_FALSE(fetcher->hasUnusedLinkPreloads());
+    EXPECT_TRUE(fetcher2->hasUnusedLinkPreloads());
+
+    // Image preload scanner on the second fetcher
+    FetchRequest fetchRequestPreloadScanner2 = FetchRequest(url, FetchInitiatorInfo());
+    Resource* imgPreloadScannerResource2 = fetcher2->requestResource(fetchRequestPreloadScanner2, TestResourceFactory(Resource::Image));
+    EXPECT_EQ(resource, imgPreloadScannerResource2);
+    EXPECT_FALSE(resource->isLinkPreload());
+    fetcher2->preloadStarted(resource);
+    EXPECT_FALSE(fetcher->hasUnusedLinkPreloads());
+    EXPECT_TRUE(fetcher2->hasUnusedLinkPreloads());
 
     // Image created by parser
     FetchRequest fetchRequest = FetchRequest(url, FetchInitiatorInfo());
     Resource* newResource = fetcher->requestResource(fetchRequest, TestResourceFactory(Resource::Image));
     Persistent<MockResourceClient> client = new MockResourceClient(newResource);
     EXPECT_EQ(resource, newResource);
     EXPECT_FALSE(resource->isLinkPreload());
+    EXPECT_FALSE(fetcher->hasUnusedLinkPreloads());
+    EXPECT_TRUE(fetcher2->hasUnusedLinkPreloads());
 
+    // Image created by parser on the second fetcher
+    FetchRequest fetchRequest2 = FetchRequest(url, FetchInitiatorInfo());
+    Resource* newResource2 = fetcher2->requestResource(fetchRequest, TestResourceFactory(Resource::Image));
+    Persistent<MockResourceClient> client2 = new MockResourceClient(newResource2);
+    EXPECT_EQ(resource, newResource2);
+    EXPECT_FALSE(resource->isLinkPreload());
+    EXPECT_FALSE(fetcher->hasUnusedLinkPreloads());
+    EXPECT_FALSE(fetcher2->hasUnusedLinkPreloads());

[Yoav Weiss, 2016/09/19 10:57:41]

This fails because the resource->isLinkPreload() is no longer true, which
doesn't decrement the counter on the second fetcher, which makes me think a
counter may be the wrong way to approach this :/

[Charlie Harrison, 2016/09/19 14:06:45]

Yeah you're right. Good thing this test showed that. To go with the counter
approach you'd have to propagate the link preload change to all fetchers. That's
a lot of complexity.

I'm willing to relax my previous push-back on the timeout, in the face of this.
What do you think Nate?

     // DCL reached on first fetcher
     EXPECT_TRUE(resource->isPreloaded());
     fetcher->clearPreloads(ResourceFetcher::ClearSpeculativeMarkupPreloads);
     Platform::current()->getURLLoaderMockFactory()->unregisterURL(url);
     EXPECT_TRUE(memoryCache()->contains(resource));
     EXPECT_TRUE(resource->isPreloaded());
 
     // DCL reached on second fetcher
     fetcher2->clearPreloads(ResourceFetcher::ClearSpeculativeMarkupPreloads);
     EXPECT_TRUE(memoryCache()->contains(resource));
     EXPECT_FALSE(resource->isPreloaded());
 }
 
 } // namespace blink