Remove SkPicture copy constructor

Given where we're heading with SkPicture why would you need to make a copy?

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

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/381133002
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 37377ae..8beb66a 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -1359,13 +1359,11 @@
     }
 
     if (kPicture_DeviceType == fDeviceType) {
-        SkAutoTUnref<SkPicture> picture(fRecorder.endRecording());
+        SkAutoTUnref<const SkPicture> picture(fRecorder.endRecording());
 
         if (true) {
-            SkPicture* pict = new SkPicture(*picture);
             this->installDrawFilter(orig);
-            orig->drawPicture(pict);
-            pict->unref();
+            orig->drawPicture(picture);
         } else if (true) {
             SkDynamicMemoryWStream ostream;
             picture->serialize(&ostream);