[win] Enable ModuleDatabase behind a flag.

chrome/browser/conflicts/module_database_win.h

 // Copyright 2016 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 CHROME_BROWSER_CONFLICTS_MODULE_DATABASE_WIN_H_
 #define CHROME_BROWSER_CONFLICTS_MODULE_DATABASE_WIN_H_
 
 #include <set>
 #include <utility>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/memory/weak_ptr.h"
 #include "base/sequenced_task_runner.h"
 #include "content/public/common/process_type.h"
 
 // A class that keeps track of all modules loaded across Chrome processes.
 // Drives the chrome://conflicts UI.
+//
+// This is effectively a singleton, but doesn't use base::Singleton. The intent
+// is for the object to be created when Chrome is single-threaded, and for it
+// be set as the process-wide singleton via SetInstance.
 class ModuleDatabase {
  public:
   // A ModuleDatabase is by default bound to a provided sequenced task runner.
   // All calls must be made in the context of this task runner, unless
   // otherwise noted. For calls from other contexts this task runner is used to
   // bounce the call when appropriate.
   explicit ModuleDatabase(scoped_refptr<base::SequencedTaskRunner> task_runner);
   ~ModuleDatabase();
 
+  // Retrieves the singleton global instance of the ModuleDatabase.
+  static ModuleDatabase* GetInstance();
+  // Sets the global instance of the ModuleDatabase.

[grt (UTC plus 2), 2017/01/06 09:44:58]

nit: blank line before comment

[chrisha, 2017/01/10 21:01:46]

Done.

+  static void SetInstance(std::unique_ptr<ModuleDatabase> module_database);
+
   // Indicates that process with the given type has started. This must be called
   // before any calls to OnModuleEvent or OnModuleUnload. Must be called in the
   // same sequence as |task_runner_|.
   void OnProcessStarted(uint32_t process_id,
                         uint64_t creation_time,
                         content::ProcessType process_type);
 
   // Indicates that a module has been loaded. The data passed to this function
   // is taken as gospel, so if it originates from a remote process it should be
   // independently validated first. (In practice, see ModuleEventSinkImpl for
@@ skipping 167 matching lines @@
   //
   // These are modified by the various static *LoadAddress* helper functions in
   // ModuleDatabase. The vector maintains the invariant the element with maximum
   // module ID is always last. This ensures that the usual operation of loading
   // a module is O(1).
   ModuleLoadAddresses loaded_modules;
   ModuleLoadAddresses unloaded_modules;
 };
 
 #endif  // CHROME_BROWSER_CONFLICTS_MODULE_DATABASE_WIN_H_