Merge to XFA: Use override in more classes in fpdfsdk/

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1287193005 .

(cherry picked from commit 0f6b51c0fdd14f5762bf3c7412ac59c825443cc3)

Review URL: https://codereview.chromium.org/1288393004 .
diff --git a/fpdfsdk/include/javascript/global.h b/fpdfsdk/include/javascript/global.h
index 303ac76..3699567 100644
--- a/fpdfsdk/include/javascript/global.h
+++ b/fpdfsdk/include/javascript/global.h
@@ -36,7 +36,7 @@
 class global_alternate : public CJS_EmbedObj {
  public:
   global_alternate(CJS_Object* pJSObject);
-  virtual ~global_alternate();
+  ~global_alternate() override;
 
  public:
   FX_BOOL setPersistent(IFXJS_Context* cc,
@@ -81,10 +81,11 @@
 
 class CJS_Global : public CJS_Object {
  public:
-  CJS_Global(JSFXObject pObject) : CJS_Object(pObject){};
-  virtual ~CJS_Global(void){};
+  explicit CJS_Global(JSFXObject pObject) : CJS_Object(pObject) {}
+  ~CJS_Global() override {}
 
-  virtual FX_BOOL InitInstance(IFXJS_Context* cc);
+  // CJS_Object
+  FX_BOOL InitInstance(IFXJS_Context* cc) override;
 
   DECLARE_SPECIAL_JS_CLASS(CJS_Global);