Avoid adding invalid headers in AddHeaderFromString

net/http/http_request_headers.h

Index: net/http/http_request_headers.h
diff --git a/net/http/http_request_headers.h b/net/http/http_request_headers.h
index 62ec37cab9f4f759df67b7ebaf971f69abcb6555..5efa5b5b7f87f15efa490b2383db11426479e49b 100644
--- a/net/http/http_request_headers.h
+++ b/net/http/http_request_headers.h
@@ -100,6 +100,8 @@ class NET_EXPORT HttpRequestHeaders {
   // Sets the header value pair for |key| and |value|.  If |key| already exists,
   // then the header value is modified, but the key is untouched, and the order
   // in the vector remains the same.  When comparing |key|, case is ignored.
+  // The caller must ensure that |key| passes HttpUtil::IsValidHeaderName() and
+  // |value| passes HttpUtil::IsValidHeaderValue().
   void SetHeader(const base::StringPiece& key, const base::StringPiece& value);
 
   // Sets the header value pair for |key| and |value|, if |key| does not exist.