Add <link rel=preconnect> support to the HTMLPreloadScanner

Source/core/html/parser/HTMLResourcePreloader.cpp

Index: Source/core/html/parser/HTMLResourcePreloader.cpp
diff --git a/Source/core/html/parser/HTMLResourcePreloader.cpp b/Source/core/html/parser/HTMLResourcePreloader.cpp
index 85d914aa64553719e8a5ca14e102a5d5566ee227..1a0314e17beffd395e40421cf2c9853e6779dfe0 100644
--- a/Source/core/html/parser/HTMLResourcePreloader.cpp
+++ b/Source/core/html/parser/HTMLResourcePreloader.cpp
@@ -29,6 +29,7 @@
 #include "core/dom/Document.h"
 #include "core/fetch/FetchInitiatorInfo.h"
 #include "core/fetch/ResourceFetcher.h"
+#include "platform/network/NetworkHints.h"
 #include "public/platform/Platform.h"
 
 namespace blink {
@@ -48,8 +49,29 @@ DEFINE_TRACE(HTMLResourcePreloader)
     visitor->trace(m_document);
 }
 
+static void preconnectHost(PreloadRequest* request)
+{
+    ASSERT(request);
+    ASSERT(request->isPreconnect());
+    KURL host(request->baseURL(), request->resourceURL());
+    if (!host.isValid())

[Mike West, 2015/06/03 09:02:27]

Perhaps add `!host.protocolIsInHTTPFamily()`? We wouldn't want to preconnect to
`data:`, for instance. What about `ws`/`wss`? Do we care about those? `ftp`?

+        return;
+    CrossOriginAttributeValue crossOrigin = CrossOriginAttributeNotSet;
+    if (request->isCORS()) {
+        if (request->isAllowCredentials())
+            crossOrigin = CrossOriginAttributeUseCredentials;

[Mike West, 2015/06/03 09:02:27]

Looking at this again, what does this actually mean in the context of
preconnect? Do we do a preflight? Do we send cookies, etc? I thought this just
warmed up the socket.

+        else
+            crossOrigin = CrossOriginAttributeAnonymous;
+    }
+    preconnect(host, crossOrigin);
+}
+
 void HTMLResourcePreloader::preload(PassOwnPtr<PreloadRequest> preload)
 {
+    if (preload->isPreconnect()) {
+        preconnectHost(preload.get());
+        return;
+    }
     FetchRequest request = preload->resourceRequest(m_document);
     Platform::current()->histogramCustomCounts("WebCore.PreloadDelayMs", static_cast<int>(1000 * (monotonicallyIncreasingTime() - preload->discoveryTime())), 0, 2000, 20);
     m_document->fetcher()->preload(preload->resourceType(), request, preload->charset());