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

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index ce90275047a6466cf9217e32bc0e9505ed8eff36..6b00443cd8ca68da752f7448dc4bd80f863016be 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -1521,6 +1521,15 @@ void SkCanvas::resetMatrix() {
     this->setMatrix(SkMatrix::I());
 }
 
+void SkCanvas::setZ(uint32_t z) {

[jvanverth1, 2016/07/07 18:43:02]

This and getZ() could be inlined directly in the SkCanvas class declaration in
SkCanvas.h

[vjiaoblack, 2016/07/07 19:04:10]

Done.

+    this->curDrawDepth = z;
+    this->didSetZ(z);
+}
+
+uint32_t SkCanvas::getZ() const {
+    return this->curDrawDepth;
+}
+
 //////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::clipRect(const SkRect& rect, SkRegion::Op op, bool doAA) {