Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/src/google/protobuf/compiler/importer.h

Index: third_party/protobuf/src/google/protobuf/compiler/importer.h
diff --git a/third_party/protobuf/src/google/protobuf/compiler/importer.h b/third_party/protobuf/src/google/protobuf/compiler/importer.h
index f010fd08b209c6a4a10c0dd3d8fd0b797de2f090..7a62fa0e66bc48d4d468dff4e2f83ff76d0685c6 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/importer.h
+++ b/third_party/protobuf/src/google/protobuf/compiler/importer.h
@@ -1,6 +1,6 @@
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
-// https://developers.google.com/protocol-buffers/
+// http://code.google.com/p/protobuf/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
@@ -166,9 +166,6 @@ class LIBPROTOBUF_EXPORT Importer {
     return &pool_;
   }
 
-  void AddUnusedImportTrackFile(const string& file_name);
-  void ClearUnusedImportTrackFiles();
-
  private:
   SourceTreeDescriptorDatabase database_;
   DescriptorPool pool_;
@@ -207,13 +204,6 @@ class LIBPROTOBUF_EXPORT SourceTree {
   // contain "." or ".." components.
   virtual io::ZeroCopyInputStream* Open(const string& filename) = 0;
 
-  // If Open() returns NULL, calling this method immediately will return an
-  // description of the error.
-  // Subclasses should implement this method and return a meaningful value for
-  // better error reporting.
-  // TODO(xiaofeng): change this to a pure virtual function.
-  virtual string GetLastErrorMessage();
-
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(SourceTree);
 };
@@ -283,9 +273,7 @@ class LIBPROTOBUF_EXPORT DiskSourceTree : public SourceTree {
   bool VirtualFileToDiskFile(const string& virtual_file, string* disk_file);
 
   // implements SourceTree -------------------------------------------
-  virtual io::ZeroCopyInputStream* Open(const string& filename);
-
-  virtual string GetLastErrorMessage();
+  io::ZeroCopyInputStream* Open(const string& filename);
 
  private:
   struct Mapping {
@@ -297,7 +285,6 @@ class LIBPROTOBUF_EXPORT DiskSourceTree : public SourceTree {
       : virtual_path(virtual_path_param), disk_path(disk_path_param) {}
   };
   vector<Mapping> mappings_;
-  string last_error_message_;
 
   // Like Open(), but returns the on-disk path in disk_file if disk_file is
   // non-NULL and the file could be successfully opened.