Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/descriptor_database.h

Index: third_party/protobuf/src/google/protobuf/descriptor_database.h
diff --git a/third_party/protobuf/src/google/protobuf/descriptor_database.h b/third_party/protobuf/src/google/protobuf/descriptor_database.h
index 2ccb1458300d218e7a977e777c586eeb723ce49f..86002d56f623fc63362580a06c3a7205b13881be 100644
--- a/third_party/protobuf/src/google/protobuf/descriptor_database.h
+++ b/third_party/protobuf/src/google/protobuf/descriptor_database.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
@@ -96,11 +96,12 @@ class LIBPROTOBUF_EXPORT DescriptorDatabase {
   //
   // This method has a default implementation that always returns
   // false.
-  virtual bool FindAllExtensionNumbers(const string& extendee_type,
-                                       vector<int>* output) {
+  virtual bool FindAllExtensionNumbers(const string& /* extendee_type */,
+                                       vector<int>* /* output */) {
     return false;
   }
 
+
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(DescriptorDatabase);
 };
@@ -311,7 +312,7 @@ class LIBPROTOBUF_EXPORT EncodedDescriptorDatabase : public DescriptorDatabase {
 // A DescriptorDatabase that fetches files from a given pool.
 class LIBPROTOBUF_EXPORT DescriptorPoolDatabase : public DescriptorDatabase {
  public:
-  DescriptorPoolDatabase(const DescriptorPool& pool);
+  explicit DescriptorPoolDatabase(const DescriptorPool& pool);
   ~DescriptorPoolDatabase();
 
   // implements DescriptorDatabase -----------------------------------
@@ -340,7 +341,7 @@ class LIBPROTOBUF_EXPORT MergedDescriptorDatabase : public DescriptorDatabase {
   // Merge more than two databases.  The sources remain property of the caller.
   // The vector may be deleted after the constructor returns but the
   // DescriptorDatabases need to stick around.
-  MergedDescriptorDatabase(const vector<DescriptorDatabase*>& sources);
+  explicit MergedDescriptorDatabase(const vector<DescriptorDatabase*>& sources);
   ~MergedDescriptorDatabase();
 
   // implements DescriptorDatabase -----------------------------------
@@ -356,6 +357,7 @@ class LIBPROTOBUF_EXPORT MergedDescriptorDatabase : public DescriptorDatabase {
   bool FindAllExtensionNumbers(const string& extendee_type,
                                vector<int>* output);
 
+
  private:
   vector<DescriptorDatabase*> sources_;
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MergedDescriptorDatabase);