SkPDF: add `final` keyword to leaf classes

src/pdf/SkPDFDevice.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPDFDevice_DEFINED
 #define SkPDFDevice_DEFINED
 
@@ skipping 26 matching lines @@
 // Private classes.
 struct ContentEntry;
 struct GraphicStateEntry;
 struct NamedDestination;
 struct RectWithData;
 
 /** \class SkPDFDevice
 
     The drawing context for the PDF backend.
 */
-class SkPDFDevice : public SkBaseDevice {
+class SkPDFDevice final : public SkBaseDevice {
 public:
     /** Create a PDF drawing context.  SkPDFDevice applies a
      *  scale-and-translate transform to move the origin from the
      *  bottom left (PDF default) to the top left (Skia default).
      *  @param pageSize Page size in point units.
      *         1 point == 127/360 mm == 1/72 inch
      *  @param rasterDpi the DPI at which features without native PDF
      *         support will be rasterized (e.g. draw image with
      *         perspective, draw text with perspective, ...).  A
      *         larger DPI would create a PDF that reflects the
@@ skipping 252 matching lines @@
 
     typedef SkBaseDevice INHERITED;
 
     // TODO(edisonn): Only SkDocument_PDF and SkPDFImageShader should be able to create
     // an SkPDFDevice
     //friend class SkDocument_PDF;
     //friend class SkPDFImageShader;
 };
 
 #endif