Bug 1294645 - Don't use NS_CALLBACK for callbacks in nsI{Input,Output,UnicharInput},Stream.idl. r=froydnj.

Slightly less than half (93 / 210) of the NS_METHOD instances in the codebase
are because of the use of NS_CALLBACK in
nsI{Input,Output,UnicharInput},Stream.idl. The use of __stdcall on Win32 isn't
important for these callbacks because they are only used as arguments to
[noscript] methods.

This patch converts them to vanilla |nsresult| functions. It increases the size
of xul.dll by about ~600 bytes, which is about 0.001%.

parser/html/nsHtml5StreamParser.cpp

@@ -1192,8 +1192,7 @@ nsHtml5StreamParser::OnDataAvailable(nsIRequest* aRequest,
   }
 }
 
-/* static */
-NS_METHOD
+/* static */ nsresult
 nsHtml5StreamParser::CopySegmentsToParser(nsIInputStream *aInStream,
                                           void *aClosure,
                                           const char *aFromSegment,