GN header checker enhancements.

tools/gn/header_checker.h

 // 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.
 
 #ifndef TOOLS_GN_HEADER_CHECKER_H_
 #define TOOLS_GN_HEADER_CHECKER_H_
 
 #include <map>
 #include <set>
 #include <vector>
@@ skipping 130 matching lines @@
                       Chain* chain,
                       bool* is_permitted) const;
 
   // For internal use by the previous override of IsDependencyOf.  If
   // require_public is true, only public dependency chains are searched.
   bool IsDependencyOf(const Target* search_for,
                       const Target* search_from,
                       bool require_permitted,
                       Chain* chain) const;
 
+  // Makes a very descriptive error message for when an include is disallowed
+  // from a given from_target, with a missing dependency to one of the given
+  // targets.
+  static Err MakeUnreachableError(const InputFile& source_file,
+                                  const LocationRange& range,
+                                  const Target* from_target,
+                                  const TargetVector& targets);
+
   // Non-locked variables ------------------------------------------------------
   //
   // These are initialized during construction (which happens on one thread)
   // and are not modified after, so any thread can read these without locking.
 
   base::MessageLoop* main_loop_;
   base::RunLoop main_thread_runner_;
 
   const BuildSettings* build_settings_;
 
   // Maps source files to targets it appears in (usually just one target).
   FileMap file_map_;
 
   // Locked variables ----------------------------------------------------------
   //
   // These are mutable during runtime and require locking.
 
   base::Lock lock_;
 
   std::vector<Err> errors_;
 
   DISALLOW_COPY_AND_ASSIGN(HeaderChecker);
 };
 
 #endif  // TOOLS_GN_HEADER_CHECKER_H_