Update //third_party/protobuf to version 3.

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 7a62fa0e66bc48d4d468dff4e2f83ff76d0685c6..cc8fcc39b09c7d55d1940a3e66c1d517c91a418e 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.
-// http://code.google.com/p/protobuf/
+// https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
@@ -121,6 +121,12 @@ class LIBPROTOBUF_EXPORT SourceTreeDescriptorDatabase : public DescriptorDatabas
                   ErrorLocation location,
                   const string& message);
 
+    virtual void AddWarning(const string& filename,
+                            const string& element_name,
+                            const Message* descriptor,
+                            ErrorLocation location,
+                            const string& message);
+
    private:
     SourceTreeDescriptorDatabase* owner_;
   };
@@ -166,6 +172,9 @@ class LIBPROTOBUF_EXPORT Importer {
     return &pool_;
   }
 
+  void AddUnusedImportTrackFile(const string& file_name);
+  void ClearUnusedImportTrackFiles();
+
  private:
   SourceTreeDescriptorDatabase database_;
   DescriptorPool pool_;
@@ -185,6 +194,9 @@ class LIBPROTOBUF_EXPORT MultiFileErrorCollector {
   virtual void AddError(const string& filename, int line, int column,
                         const string& message) = 0;
 
+  virtual void AddWarning(const string& filename, int line, int column,
+                          const string& message) {}
+
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MultiFileErrorCollector);
 };
@@ -204,6 +216,13 @@ 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);
 };
@@ -273,7 +292,9 @@ class LIBPROTOBUF_EXPORT DiskSourceTree : public SourceTree {
   bool VirtualFileToDiskFile(const string& virtual_file, string* disk_file);
 
   // implements SourceTree -------------------------------------------
-  io::ZeroCopyInputStream* Open(const string& filename);
+  virtual io::ZeroCopyInputStream* Open(const string& filename);
+
+  virtual string GetLastErrorMessage();
 
  private:
   struct Mapping {
@@ -285,6 +306,7 @@ 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.