Provide a std::vector compliant empty() method for WebVector.

third_party/WebKit/Source/core/loader/DocumentLoader.cpp

Index: third_party/WebKit/Source/core/loader/DocumentLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/DocumentLoader.cpp b/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
index b8767260da3b54447598a4982e67326047400931..dda86188366c8fd96316df78485dd773dbaa2d60 100644
--- a/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
@@ -1026,7 +1026,7 @@ void setFeaturePolicy(Document* document, const String& featurePolicyHeader) {
         ConsoleMessage::create(OtherMessageSource, ErrorMessageLevel,
                                "Error with Feature-Policy header: " + message));
   }
-  if (!parsedHeader.isEmpty())
+  if (!parsedHeader.empty())
     frame->client()->didSetFeaturePolicyHeader(parsedHeader);
 }