Added the framework for having canvas/recorder/picture record depth_set's.

src/core/SkRecorder.h

Index: src/core/SkRecorder.h
diff --git a/src/core/SkRecorder.h b/src/core/SkRecorder.h
index 1299efbdd6deee419e718dd01cee22dc393080b2..53c9c6618e5c166becb59853c60fe97224b3454a 100644
--- a/src/core/SkRecorder.h
+++ b/src/core/SkRecorder.h
@@ -60,6 +60,7 @@ public:
 
     void didConcat(const SkMatrix&) override;
     void didSetMatrix(const SkMatrix&) override;
+    void didSetZ(const uint32_t) override;
 
     void onDrawDRRect(const SkRRect&, const SkRRect&, const SkPaint&) override;
     void onDrawDrawable(SkDrawable*, const SkMatrix*) override;