Fix more clang/win plugin warnings after GDI font emulation CL.

content/common/font_warmup_win_unittest.cc

Index: content/common/font_warmup_win_unittest.cc
diff --git a/content/common/font_warmup_win_unittest.cc b/content/common/font_warmup_win_unittest.cc
index 44bb96a5698fb511716add60b98e1ac2e6d54d06..80eb9e57b1f83f7dc33c94ac27f28dc8f7876a22 100644
--- a/content/common/font_warmup_win_unittest.cc
+++ b/content/common/font_warmup_win_unittest.cc
@@ -132,7 +132,9 @@ const wchar_t* kTestFontFamilyInvalid = L"InvalidFont";
 class TestSkFontMgr : public SkFontMgr {
  public:
   TestSkFontMgr() { content::SetPreSandboxWarmupFontMgrForTesting(this); }
-  ~TestSkFontMgr() { content::SetPreSandboxWarmupFontMgrForTesting(nullptr); }
+  ~TestSkFontMgr() override {
+    content::SetPreSandboxWarmupFontMgrForTesting(nullptr);
+  }
 
  protected:
   int onCountFamilies() const override { return 1; }