Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/mediastream/UserMediaRequest.cpp

Index: Source/modules/mediastream/UserMediaRequest.cpp
diff --git a/Source/modules/mediastream/UserMediaRequest.cpp b/Source/modules/mediastream/UserMediaRequest.cpp
index 452168ed904e42cdf088d69420f4077918f7c632..750298b508f5e93ddc3867dcbf38f34b21b63c88 100644
--- a/Source/modules/mediastream/UserMediaRequest.cpp
+++ b/Source/modules/mediastream/UserMediaRequest.cpp
@@ -67,14 +67,14 @@ PassRefPtr<UserMediaRequest> UserMediaRequest::create(ExecutionContext* context,
 {
     blink::WebMediaConstraints audio = parseOptions(options, "audio", exceptionState);
     if (exceptionState.hadException())
-        return 0;
+        return nullptr;
 
     blink::WebMediaConstraints video = parseOptions(options, "video", exceptionState);
     if (exceptionState.hadException())
-        return 0;
+        return nullptr;
 
     if (audio.isNull() && video.isNull())
-        return 0;
+        return nullptr;
 
     return adoptRef(new UserMediaRequest(context, controller, audio, video, successCallback, errorCallback));
 }