Add WebPrescientNetworking to trigger preconnect from Blink.

Source/Platform/chromium/public/WebPrerenderingSupport.h

Index: Source/Platform/chromium/public/WebPrerenderingSupport.h
diff --git a/Source/Platform/chromium/public/WebPrerenderingSupport.h b/Source/Platform/chromium/public/WebPrerenderingSupport.h
index a2672911fa50a83358d2bf4b0996fd5493806ba2..b50d6afe2fc45d35bf26a8f91390dc5a20a32c8d 100644
--- a/Source/Platform/chromium/public/WebPrerenderingSupport.h
+++ b/Source/Platform/chromium/public/WebPrerenderingSupport.h
@@ -32,10 +32,12 @@
 #define WebPrerenderingSupport_h
 
 #include "WebCommon.h"
+#include "WebPreconnectMotivation.h"
 
 namespace WebKit {
 
 class WebPrerender;
+class WebURL;
 
 class WebPrerenderingSupport {
 public:
@@ -43,6 +45,10 @@ public:
     WEBKIT_EXPORT static void shutdown();
     WEBKIT_EXPORT static WebPrerenderingSupport* current();
 
+    // preconnect to the host providing resource specified by given url.

[tkent, 2013/05/08 23:12:47]

It's hard to understand this comment.
What does this function do concretely? When should we call this? What is 'host'?

nit: a comment should start a capital letter.

+    virtual void preconnect(const WebURL& url,
+                            WebPreconnectMotivation motivation) = 0;
+
     // A prerender link element is added when it is inserted into a document.
     virtual void add(const WebPrerender&) = 0;