Add WebPrescientNetworking to trigger preconnect from Blink.

Source/Platform/chromium/public/Platform.h

Index: Source/Platform/chromium/public/Platform.h
diff --git a/Source/Platform/chromium/public/Platform.h b/Source/Platform/chromium/public/Platform.h
index 39eea50589c119086ec1772266261372d185d686..566305709c633907bf65e267ca185e78e0b2df96 100644
--- a/Source/Platform/chromium/public/Platform.h
+++ b/Source/Platform/chromium/public/Platform.h
@@ -68,6 +68,7 @@ class WebMediaStreamCenterClient;
 class WebMessagePortChannel;
 class WebMimeRegistry;
 class WebPluginListBuilder;
+class WebPrescientNetworking;
 class WebRTCPeerConnectionHandler;
 class WebRTCPeerConnectionHandlerClient;
 class WebSandboxSupport;
@@ -268,6 +269,9 @@ public:
     // A suggestion to prefetch IP information for the given hostname.
     virtual void prefetchHostName(const WebString&) { }
 
+    // May return null.
+    virtual WebPrescientNetworking* prescientNetworking() { return 0; }
+
     // Returns a new WebSocketStreamHandle instance.
     virtual WebSocketStreamHandle* createSocketStreamHandle() { return 0; }