headless: Add error reporter utility

headless/public/util/error_reporter.h

Index: headless/public/util/error_reporter.h
diff --git a/headless/public/util/error_reporter.h b/headless/public/util/error_reporter.h
new file mode 100644
index 0000000000000000000000000000000000000000..d7eb5e96d2148a881c6c86ad3a87f341119ff0e6
--- /dev/null
+++ b/headless/public/util/error_reporter.h
@@ -0,0 +1,48 @@
+// Copyright 2016 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.
+
+#ifndef HEADLESS_PUBLIC_UTIL_ERROR_REPORTER_H_
+#define HEADLESS_PUBLIC_UTIL_ERROR_REPORTER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/strings/string_piece.h"
+#include "headless/public/headless_export.h"
+
+namespace headless {
+
+// Tracks errors which are encountered while parsing client API types.
+class HEADLESS_EXPORT ErrorReporter {
+ public:
+  ErrorReporter();
+  ~ErrorReporter();
+
+  // Enter a new nested parsing context. It will initially have a null name.
+  void Push();
+
+  // Leave the current parsing context, returning to the previous one.
+  void Pop();
+
+  // Set the name of the current parsing context. |name| must be a string with
+  // application lifetime.
+  void SetName(const char* name);
+
+  // Report an error in the current parsing context.
+  void AddError(base::StringPiece description);
+
+  // Returns true if any errors have been reported so far.
+  bool HasErrors() const;
+
+  // Returns a list of reported errors.
+  const std::vector<std::string>& errors() const { return errors_; }
+
+ private:
+  std::vector<const char*> path_;
+  std::vector<std::string> errors_;
+};
+
+}  // namespace headless
+
+#endif  // HEADLESS_PUBLIC_UTIL_ERROR_REPORTER_H_