Mark overridden destructors with 'override' and remove 'virtual'

This silences a new warning in clang 5.0

Change-Id: Ieb5b75a6ffed60107c3fd16075d2ecfd515b55e8
Reviewed-on: https://skia-review.googlesource.com/10006
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/src/gpu/ops/GrOvalOpFactory.cpp b/src/gpu/ops/GrOvalOpFactory.cpp
index 8ab33f5..dbab985 100644
--- a/src/gpu/ops/GrOvalOpFactory.cpp
+++ b/src/gpu/ops/GrOvalOpFactory.cpp
@@ -103,7 +103,7 @@
 
     bool implementsDistanceVector() const override { return !fInClipPlane; }
 
-    virtual ~CircleGeometryProcessor() {}
+    ~CircleGeometryProcessor() override {}
 
     const char* name() const override { return "CircleEdge"; }
 
@@ -274,7 +274,7 @@
         fStroke = stroke;
     }
 
-    virtual ~EllipseGeometryProcessor() {}
+    ~EllipseGeometryProcessor() override {}
 
     const char* name() const override { return "EllipseEdge"; }
 
@@ -416,7 +416,7 @@
         fStyle = style;
     }
 
-    virtual ~DIEllipseGeometryProcessor() {}
+    ~DIEllipseGeometryProcessor() override {}
 
     const char* name() const override { return "DIEllipseEdge"; }