Alter SkCanvas::drawPicture (devirtualize, take const SkPicture, take pointer)

R=reed@google.com, bsalomon@google.com, mtklein@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/313613004
diff --git a/include/gpu/SkGpuDevice.h b/include/gpu/SkGpuDevice.h
index f2a27d7..c9650d6 100644
--- a/include/gpu/SkGpuDevice.h
+++ b/include/gpu/SkGpuDevice.h
@@ -152,11 +152,11 @@
     virtual bool onWritePixels(const SkImageInfo&, const void*, size_t, int, int) SK_OVERRIDE;
 
     /**  PRIVATE / EXPERIMENTAL -- do not call */
-    virtual void EXPERIMENTAL_optimize(SkPicture* picture) SK_OVERRIDE;
+    virtual void EXPERIMENTAL_optimize(const SkPicture* picture) SK_OVERRIDE;
     /**  PRIVATE / EXPERIMENTAL -- do not call */
-    virtual void EXPERIMENTAL_purge(SkPicture* picture) SK_OVERRIDE;
+    virtual void EXPERIMENTAL_purge(const SkPicture* picture) SK_OVERRIDE;
     /**  PRIVATE / EXPERIMENTAL -- do not call */
-    virtual bool EXPERIMENTAL_drawPicture(SkCanvas* canvas, SkPicture* picture) SK_OVERRIDE;
+    virtual bool EXPERIMENTAL_drawPicture(SkCanvas* canvas, const SkPicture* picture) SK_OVERRIDE;
 
 private:
     GrContext*      fContext;