Use "override" keyword instead of "virtual".

"override" provides a compile-time gaurantee that the function is indeed
overriding a virtual function. This prevents the potential mistake of
creating a new virtual function rather than overriding the original.

I happened to notice we could use "override" here instead of "virtual".
Might as well tidy up a bit.

Test: Built locally
BUG=115613038

Change-Id: I7f43f4a466d8ceaa1b863d6a2af054e69618d0c8

native/webview/plat_support/draw_gl_functor.cpp

@@ -42,10 +42,10 @@ AwDrawGLFunction* g_aw_drawgl_function = NULL;
 class DrawGLFunctor : public Functor {
  public:
   explicit DrawGLFunctor(jlong view_context) : view_context_(view_context) {}
-  virtual ~DrawGLFunctor() {}
+  ~DrawGLFunctor() override {}
 
   // Functor
-  virtual status_t operator ()(int what, void* data) {
+  status_t operator ()(int what, void* data) override {
     using uirenderer::DrawGlInfo;
     if (!g_aw_drawgl_function) {
       ALOGE("Cannot draw: no DrawGL Function installed");