GN: Move towards only using / on Windows

tools/gn/source_file.cc

Index: tools/gn/source_file.cc
diff --git a/tools/gn/source_file.cc b/tools/gn/source_file.cc
index e5d67753e7f4a958bf09542fd3ead162ae94bcf8..1bbee2458f9882957bb6eaa4b61756645cd41f39 100644
--- a/tools/gn/source_file.cc
+++ b/tools/gn/source_file.cc
@@ -53,11 +53,10 @@ base::FilePath SourceFile::Resolve(const base::FilePath& source_root) const {
     } else {
       converted.assign(value_);
     }
-    ConvertPathToSystem(&converted);
     return base::FilePath(UTF8ToFilePath(converted));
   }
 
   converted.assign(&value_[2], value_.size() - 2);
-  ConvertPathToSystem(&converted);
-  return source_root.Append(UTF8ToFilePath(converted));
+  return source_root.Append(UTF8ToFilePath(converted))
+      .NormalizePathSeparatorsTo(L'/');
 }