Don't wait for AppCache for link rel preloads

third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp

Index: third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp b/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
index 22a7b2c3460f4f538969c9386f73956e55e41959..4958ff44bf5ec9a106c9da7283184fc267b12d13 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -298,17 +298,25 @@ void HTMLDocumentParser::notifyPendingParsedChunks()
 
     // ApplicationCache needs to be initialized before issuing preloads.
     // We suspend preload until HTMLHTMLElement is inserted and
-    // ApplicationCache is initialized.
+    // ApplicationCache is initialized. Note: link rel preloads don't follow
+    // this policy per the spec. These directives should initiate a fetch as
+    // fast as possible.
     if (!document()->documentElement()) {
+        PreloadRequestStream linkRelPreloads;
         for (auto& chunk : pendingChunks) {
-            for (auto& request : chunk->preloads)
-                m_queuedPreloads.append(std::move(request));
+            for (auto& request : chunk->preloads) {

[Yoav Weiss, 2016/07/22 08:43:28]

I don't understand why this waiting is necessary for *any* resource. The
preloadScanner bails out from preloading if AppCache is present. So AFAIUI if we
have preloads here, there's no AppCache.

[Charlie Harrison, 2016/07/22 14:03:22]

My understanding is that the preload scanner just looks for the manifest
attribute on the html element, but I think you can have appcache enabled even
without that check. Looking over the code right now
(WebApplicationCacheHostImpl::selectCacheWithoutManifest) it looks like this
might only happen if the document you loaded was loaded via appcache? Kouhei, do
you have more context for this?

+                if (request->isLinkRelPreload())
+                    linkRelPreloads.append(std::move(request));
+                else
+                    m_queuedPreloads.append(std::move(request));
+            }
             for (auto& index : chunk->likelyDocumentWriteScriptIndices) {
                 const CompactHTMLToken& token = chunk->tokens->at(index);
                 ASSERT(token.type() == HTMLToken::TokenType::Character);
                 m_queuedDocumentWriteScripts.append(token.data());
             }
         }
+        m_preloader->takeAndPreload(linkRelPreloads);
     } else {
         // We can safely assume that there are no queued preloads request after
         // the document element is available, as we empty the queue immediately
@@ -469,13 +477,11 @@ size_t HTMLDocumentParser::processParsedChunkFromBackgroundParser(std::unique_pt
             break;
 
         if (!m_triedLoadingLinkHeaders && document()->loader()) {
-            String linkHeader = document()->loader()->response().httpHeaderField(HTTPNames::Link);
-            if (!linkHeader.isEmpty()) {
-                ASSERT(chunk);
-                LinkLoader::loadLinksFromHeader(linkHeader, document()->loader()->response().url(),
-                    document(), NetworkHintsInterfaceImpl(), LinkLoader::OnlyLoadResources, &(chunk->viewport));
-                m_triedLoadingLinkHeaders = true;
-            }
+            DCHECK(chunk);
+            // Note that on commit, the loader dispatched preloads for all the
+            // non-media links.
+            document()->loader()->dispatchLinkHeaderPreloads(&chunk->viewport, LinkLoader::OnlyLoadMedia);
+            m_triedLoadingLinkHeaders = true;
         }
 
         if (isWaitingForScripts()) {