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

tools/debugger/SkDebugCanvas.cpp

Index: tools/debugger/SkDebugCanvas.cpp
diff --git a/tools/debugger/SkDebugCanvas.cpp b/tools/debugger/SkDebugCanvas.cpp
index ceea78219314015752baaf578168ac1a319fed41..feaa9badb907608a3cd0ae088982efe04b6a52c1 100644
--- a/tools/debugger/SkDebugCanvas.cpp
+++ b/tools/debugger/SkDebugCanvas.cpp
@@ -685,6 +685,11 @@ void SkDebugCanvas::didSetMatrix(const SkMatrix& matrix) {
     this->INHERITED::didSetMatrix(matrix);
 }
 
+void SkDebugCanvas::didSetZ(SkScalar z) {
+    this->addDrawCommand(new SkSetZCommand(z));
+    this->INHERITED::didSetZ(z);
+}
+
 void SkDebugCanvas::toggleCommand(int index, bool toggle) {
     SkASSERT(index < fCommandVector.count());
     fCommandVector[index]->setVisible(toggle);