tools/gn: Fix errors found by Facebook's flint tool.

tools/gn/builder.h

 // Copyright (c) 2013 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_BUILDER_H_
 #define TOOLS_GN_BUILDER_H_
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/memory/ref_counted.h"
 #include "tools/gn/builder_record.h"
 #include "tools/gn/label.h"
 #include "tools/gn/label_ptr.h"
 #include "tools/gn/unique_vector.h"
 
 class Config;
 class Err;
 class Loader;
 class ParseNode;
 
 class Builder : public base::RefCountedThreadSafe<Builder> {
  public:
   typedef base::Callback<void(const BuilderRecord*)> ResolvedCallback;
 
-  Builder(Loader* loader);
+  explicit Builder(Loader* loader);
 
   // The resolved callback is called whenever a target has been resolved. This
   // will be executed only on the main thread.
   void set_resolved_callback(const ResolvedCallback& cb) {
     resolved_callback_ = cb;
   }
 
   Loader* loader() const { return loader_; }
 
   void ItemDefined(scoped_ptr<Item> item);
@@ skipping 95 matching lines @@
   // Owning pointers.
   typedef base::hash_map<Label, BuilderRecord*> RecordMap;
   RecordMap records_;
 
   ResolvedCallback resolved_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(Builder);
 };
 
 #endif  // TOOLS_GN_BUILDER_H_