Update code to use helper function for better readability/searching.

src/ports/SkXMLParser_expat.cpp

Index: src/ports/SkXMLParser_expat.cpp
diff --git a/src/ports/SkXMLParser_expat.cpp b/src/ports/SkXMLParser_expat.cpp
index afc9f79fb5d73f3a8bcbd8f5807cdad1ef7496bb..3eba2fe8e0c4d0faae3e6cac99fc3b64bddd4f60 100644
--- a/src/ports/SkXMLParser_expat.cpp
+++ b/src/ports/SkXMLParser_expat.cpp
@@ -113,7 +113,7 @@ bool SkXMLParser::parse(const char doc[], size_t len)
 
 bool SkXMLParser::parse(SkStream& input)
 {
-    size_t          len = input.read(NULL, 0);
+    size_t          len = input.getLength();
     SkAutoMalloc    am(len);
     char*           doc = (char*)am.get();