Issue #1652, #3456 - Replace 's_asyncWebBrowser2' with thread-safe facilities

src/plugin/PluginClass.h

Index: src/plugin/PluginClass.h
===================================================================
--- a/src/plugin/PluginClass.h
+++ b/src/plugin/PluginClass.h
@@ -28,7 +28,7 @@
 #define _CRTDBG_MAP_ALLOC
 #include <stdlib.h>
 #include <crtdbg.h>
-#include <set>
+#include <mutex>
 
 #include "NotificationMessage.h"
 
@@ -51,6 +51,7 @@
 {
 
   friend class CPluginTab;
+  friend class AnyCurrentSiteBrowser;
 
 private:
 
@@ -103,7 +104,6 @@
 public:
   HWND GetBrowserHWND() const;
   bool IsRootBrowser(IWebBrowser2*);
-
   static CPluginMimeFilterClient* s_mimeFilter;
 
 private:
@@ -136,7 +136,6 @@
   void Unadvise();
 
   void ShowStatusBar();
-  bool IsStatusBarEnabled();
 
   /**
    * A browser interface pointer to our site object
@@ -144,6 +143,11 @@
    * It's values are set and reset solely in SetSite().
    */
   CComPtr<IWebBrowser2> m_webBrowser2;
+  /**
+   * Synchronizes SetSite() with references to our site pointer.

[sergei, 2016/01/04 15:34:31]

I would like to have here a little bit extended comment that it can be used, for
example, to avoid any wrong usage of injected objects beyond the time span
between SetSite(not nullptr) and SetSite(nullptr). For example,
AnyCurrentSiteBrowser helps to  achieve it.

[Eric, 2016/01/04 17:49:20]

There's nothing I could add here that's not fully explained in the
already-extensive comments for 'AnyCurrentSiteBrowser'.

The term "synchronizes with" is jargon from the C++ language standard. I'm
assuming a reader knows that. With that in mind, the comment completely explains
what this member variable does.

You seem to be looking for "how it's used" comments, but those are elsewhere.

+   */
+  std::mutex siteGuard;
+
   HWND m_hBrowserWnd;
   HWND m_hTabWnd;
   HWND m_hStatusBarWnd;
@@ -176,14 +180,9 @@
   static bool s_isMainThreadDone;
 
   static HINSTANCE s_hUxtheme;
-  static std::set<CPluginClass*> s_instances;
   static std::map<DWORD,CPluginClass*> s_threadInstances;
   static CComAutoCriticalSection s_criticalSectionLocal;
   static CComAutoCriticalSection s_criticalSectionWindow;
-
-  // Async browser
-  static CComQIPtr<IWebBrowser2> s_asyncWebBrowser2;
-  static CComQIPtr<IWebBrowser2> GetAsyncBrowser();
 };
 
 OBJECT_ENTRY_AUTO(__uuidof(PluginClass), CPluginClass)