GN: Make file/dir resolving return errors.

tools/gn/command_format.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <sstream>
 
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/strings/string_split.h"
 #include "tools/gn/commands.h"
@@ skipping 994 matching lines @@
   // should all be done in parallel.
   if (args.size() != 1) {
     Err(Location(), "Expecting exactly one argument, see `gn help format`.\n")
         .PrintToStdout();
     return 1;
   }
 
   Setup setup;
   SourceDir source_dir =
       SourceDirForCurrentDirectory(setup.build_settings().root_path());
-  SourceFile file = source_dir.ResolveRelativeFile(args[0]);
+
+  Err err;
+  SourceFile file = source_dir.ResolveRelativeFile(Value(nullptr, args[0]),
+                                                   &err);
+  if (err.has_error()) {
+    err.PrintToStdout();
+    return 1;
+  }
 
   std::string output_string;
   if (FormatFileToString(&setup, file, dump_tree, &output_string)) {
     if (in_place) {
       base::FilePath to_write = setup.build_settings().GetFullPath(file);
       std::string original_contents;
       if (!base::ReadFileToString(to_write, &original_contents)) {
         Err(Location(), std::string("Couldn't read \"") +
                             to_write.AsUTF8Unsafe() +
                             std::string("\" for comparison.")).PrintToStdout();
@@ skipping 14 matching lines @@
       }
     } else {
       printf("%s", output_string.c_str());
     }
   }
 
   return 0;
 }
 
 }  // namespace commands