Make an include path relative to src/

NOTRY=true

Review URL: https://codereview.chromium.org/54983009

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 99bcf0225b93f9a2820a7c1f5fd4e9b1ad9f2923
diff --git a/tools/gn/input_conversion.cc b/tools/gn/input_conversion.cc
index c40bdba..efdff1a 100644
--- a/tools/gn/input_conversion.cc
+++ b/tools/gn/input_conversion.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "input_conversion.h"
+#include "tools/gn/input_conversion.h"
 
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"