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

tools/gn/scope.cc

 // 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.
 
 #include "tools/gn/scope.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/template.h"
 
 namespace {
 
 // FLags set in the mode_flags_ of a scope. If a bit is set, it applies
 // recursively to all dependent scopes.
 const unsigned kProcessingBuildConfigFlag = 1;
 const unsigned kProcessingImportFlag = 2;
 
 // Returns true if this variable name should be considered private. Private
 // values start with an underscore, and are not imported from "gni" files
 // when processing an import.
 bool IsPrivateVar(const base::StringPiece& name) {
   return name.empty() || name[0] == '_';
 }
 
 }  // namespace
 
+
+Scope::ProgrammaticProvider::~ProgrammaticProvider() {
+  scope_->RemoveProvider(this);
+}
+
 Scope::Scope(const Settings* settings)
     : const_containing_(nullptr),
       mutable_containing_(nullptr),
       settings_(settings),
       mode_flags_(0),
       item_collector_(nullptr) {
 }
 
 Scope::Scope(Scope* parent)
     : const_containing_(nullptr),
@@ skipping 425 matching lines @@
 }
 
 void Scope::AddProvider(ProgrammaticProvider* p) {
   programmatic_providers_.insert(p);
 }
 
 void Scope::RemoveProvider(ProgrammaticProvider* p) {
   DCHECK(programmatic_providers_.find(p) != programmatic_providers_.end());
   programmatic_providers_.erase(p);
 }