Fix Up SingletonHwnd Observer Lifetime Issues

ui/gfx/font_render_params_win.cc

Index: ui/gfx/font_render_params_win.cc
diff --git a/ui/gfx/font_render_params_win.cc b/ui/gfx/font_render_params_win.cc
index 5709feab4c939eaae776aca1880c9e91fef77375..7c9c7d9c17f3f6f33a84f487041fc5abde2eaf62 100644
--- a/ui/gfx/font_render_params_win.cc
+++ b/ui/gfx/font_render_params_win.cc
@@ -2,6 +2,8 @@
 // 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"
@@ -42,7 +44,7 @@ FontRenderParams::SubpixelRendering GetSubpixelRenderingGeometry() {
 }
 
 // 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();
@@ -72,7 +74,9 @@ class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
         params_->subpixel_rendering = GetSubpixelRenderingGeometry();
       }
     }
-    gfx::SingletonHwnd::GetInstance()->AddObserver(this);
+    singletonHwndObserver_.SetWndProc(
+        base::Bind(&CachedFontRenderParams::OnSettingsChange,
+                   base::Unretained(this)));
     return *params_;
   }
 
@@ -85,17 +89,15 @@ class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
     // 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);
 };