Make calls to AtomicString(const String&) explicit in loader/ and fetch/

Source/core/loader/PingLoader.cpp

Index: Source/core/loader/PingLoader.cpp
diff --git a/Source/core/loader/PingLoader.cpp b/Source/core/loader/PingLoader.cpp
index 5e1778296bc934eed982011f33968b175e6e9ad6..fec82c8f6c117e6d56301c9909415c2c9941698d 100644
--- a/Source/core/loader/PingLoader.cpp
+++ b/Source/core/loader/PingLoader.cpp
@@ -85,12 +85,12 @@ void PingLoader::sendPing(Frame* frame, const KURL& pingURL, const KURL& destina
     if (frame->document()->securityOrigin()->isSameSchemeHostPort(pingOrigin.get()))
         request.clearHTTPReferrer();
 
-    request.setHTTPHeaderField("Ping-To", destinationURL.string());
+    request.setHTTPHeaderField("Ping-To", AtomicString(destinationURL.string()));
 
     // Ping-From follows the same rules as the default referrer beahavior for subresource requests.
     // FIXME: Should Ping-From obey ReferrerPolicy?
     if (!SecurityPolicy::shouldHideReferrer(pingURL, frame->document()->url().string()))
-        request.setHTTPHeaderField("Ping-From", frame->document()->url().string());
+        request.setHTTPHeaderField("Ping-From", AtomicString(frame->document()->url().string()));
     OwnPtr<PingLoader> pingLoader = adoptPtr(new PingLoader(frame, request));
 
     // Leak the ping loader, since it will kill itself as soon as it receives a response.