Remove default charset of dataURL request

net/base/data_url.cc

Index: net/base/data_url.cc
diff --git a/net/base/data_url.cc b/net/base/data_url.cc
index 40911850ff39e1dac100a7ee5a4fa2eaedce6e43..b9d89bfa4d5f5e2151ef45d054640d2c35173ec2 100644
--- a/net/base/data_url.cc
+++ b/net/base/data_url.cc
@@ -77,10 +77,7 @@ bool DataURL::Parse(const GURL& url, std::string* mime_type,
     // value is invalid. For this case, we don't respect |charset| but force it
     // set to "US-ASCII".
     mime_type->assign("text/plain");
-    charset->assign("US-ASCII");
   }
-  if (charset->empty())
-    charset->assign("US-ASCII");
 
   // The caller may not be interested in receiving the data.
   if (!data)