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

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index ec14829ca85296d12d79d27a04073c6ee587c20e..6aa7b5492f7a15d77cf255327088d0208f1865c9 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -444,6 +444,16 @@ public:
     */
     void resetMatrix();
 
+    /** Set the current draw depth of the canvas.

[robertphillips, 2016/07/08 17:26:43]

Fix this comment

[vjiaoblack, 2016/07/11 18:04:42]

Done.

+        @param z    The integer depth, intended between 0 - 255 inclusive
+                    0 is lowest (into screen), 255 is highest (out of screen)

[robertphillips, 2016/07/08 17:26:43]

Add info that this plays in the save/restore stack.

[vjiaoblack, 2016/07/11 18:04:42]

Done.

+    */
+    void setZ(SkScalar z);
+
+    /** Returns the current draw depth of the canvas.
+    */

[robertphillips, 2016/07/08 17:26:43]

Fix return value

[vjiaoblack, 2016/07/11 18:04:42]

Done.

+    uint32_t getZ() const;
+
     /**
      *  Modify the current clip with the specified rectangle.
      *  @param rect The rect to combine with the current clip
@@ -1307,6 +1317,7 @@ protected:
     virtual void didRestore() {}
     virtual void didConcat(const SkMatrix&) {}
     virtual void didSetMatrix(const SkMatrix&) {}

[robertphillips, 2016/07/08 17:26:42]

don't need const on a scalar

[vjiaoblack, 2016/07/11 18:04:42]

Done.

+    virtual void didSetZ(const SkScalar) {}
 
     virtual void onDrawAnnotation(const SkRect&, const char key[], SkData* value);
     virtual void onDrawDRRect(const SkRRect&, const SkRRect&, const SkPaint&);