Fix Up SingletonHwnd Observer Lifetime Issues

ui/gfx/font_render_params_win.cc

 // Copyright 2014 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 "base/bind.h"
+#include "base/bind_helpers.h"
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "base/win/registry.h"
 #include "ui/gfx/font_render_params.h"
 #include "ui/gfx/win/direct_write.h"
 #include "ui/gfx/win/singleton_hwnd.h"
 
 namespace gfx {
 
@@ skipping 20 matching lines @@
       }
       break;
     }
   }
 
   // No explicit ClearType settings, default to RGB.
   return FontRenderParams::SUBPIXEL_RENDERING_RGB;
 }
 
 // Caches font render params and updates them on system notifications.
-class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
+class CachedFontRenderParams {
  public:
   static CachedFontRenderParams* GetInstance() {
     return Singleton<CachedFontRenderParams>::get();
   }
 
   const FontRenderParams& GetParams() {
     if (params_)
       return *params_;
 
     params_.reset(new FontRenderParams());
     params_->antialiasing = false;
     params_->subpixel_positioning = false;
     params_->autohinter = false;
     params_->use_bitmaps = false;
     params_->hinting = FontRenderParams::HINTING_MEDIUM;
     params_->subpixel_rendering = FontRenderParams::SUBPIXEL_RENDERING_NONE;
 
     BOOL enabled = false;
     if (SystemParametersInfo(SPI_GETFONTSMOOTHING, 0, &enabled, 0) && enabled) {
       params_->antialiasing = true;
       // GDI does not support subpixel positioning.
       params_->subpixel_positioning = win::IsDirectWriteEnabled();
 
       UINT type = 0;
       if (SystemParametersInfo(SPI_GETFONTSMOOTHINGTYPE, 0, &type, 0) &&
           type == FE_FONTSMOOTHINGCLEARTYPE) {
         params_->subpixel_rendering = GetSubpixelRenderingGeometry();
       }
     }
-    gfx::SingletonHwnd::GetInstance()->AddObserver(this);
+    singletonHwndObserver_.SetWndProc(
+        base::Bind(&CachedFontRenderParams::OnSettingsChange,
+                   base::Unretained(this)));
     return *params_;
   }
 
  private:
   friend struct DefaultSingletonTraits<CachedFontRenderParams>;
 
   CachedFontRenderParams() {}
   virtual ~CachedFontRenderParams() {
     // Can't remove the SingletonHwnd observer here since SingletonHwnd may have
     // been destroyed already (both singletons).
   }
 
-  void OnWndProc(HWND hwnd,
-                 UINT message,
-                 WPARAM wparam,
-                 LPARAM lparam) override {
+  void OnSettingsChange(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) {
     if (message == WM_SETTINGCHANGE) {
       params_.reset();
-      gfx::SingletonHwnd::GetInstance()->RemoveObserver(this);
+      singletonHwndObserver_.ClearWndProc();
     }
   }
 
   scoped_ptr<FontRenderParams> params_;
+  SingletonHwnd::Observer singletonHwndObserver_;
 
   DISALLOW_COPY_AND_ASSIGN(CachedFontRenderParams);
 };
 
 }  // namespace
 
 FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
                                      std::string* family_out) {
   if (family_out)
     NOTIMPLEMENTED();
   // Customized font rendering settings are not supported, only defaults.
   return CachedFontRenderParams::GetInstance()->GetParams();
 }
 
 }  // namespace gfx