Make Document.charset an alias of characterSet, as per spec

third_party/WebKit/Source/core/dom/ProcessingInstruction.cpp

Index: third_party/WebKit/Source/core/dom/ProcessingInstruction.cpp
diff --git a/third_party/WebKit/Source/core/dom/ProcessingInstruction.cpp b/third_party/WebKit/Source/core/dom/ProcessingInstruction.cpp
index cbe3e6c9c66a70d77e877de0e59c18b746d7f388..d540c30237fafccc249aee9cdd48323fe3ec2988 100644
--- a/third_party/WebKit/Source/core/dom/ProcessingInstruction.cpp
+++ b/third_party/WebKit/Source/core/dom/ProcessingInstruction.cpp
@@ -172,7 +172,7 @@ void ProcessingInstruction::process(const String& href, const String& charset)
         if (RuntimeEnabledFeatures::xsltEnabled())
             resource = XSLStyleSheetResource::fetch(request, document().fetcher());
     } else {
-        request.setCharset(charset.isEmpty() ? document().charset() : charset);
+        request.setCharset(charset.isEmpty() ? document().characterSet() : charset);
         resource = CSSStyleSheetResource::fetch(request, document().fetcher());
     }