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

src/core/SkPictureRecord.cpp

Index: src/core/SkPictureRecord.cpp
diff --git a/src/core/SkPictureRecord.cpp b/src/core/SkPictureRecord.cpp
index 4a6ece17f25a8ce864601ffd706cdf2ebb4aa42a..82977b0db4e56ff79ea0fe6db4b769256a046127 100644
--- a/src/core/SkPictureRecord.cpp
+++ b/src/core/SkPictureRecord.cpp
@@ -218,6 +218,15 @@ void SkPictureRecord::didSetMatrix(const SkMatrix& matrix) {
     this->INHERITED::didSetMatrix(matrix);
 }
 
+void SkPictureRecord::didSetZ(const SkScalar z) {
+    this->validate(fWriter.bytesWritten(), 0);
+    // set Z
+    size_t size = sizeof(SkScalar);
+    size_t initialOffset = this->addDraw(SET_Z, &size);
+
+    this->validate(initialOffset, size);
+}
+
 static bool regionOpExpands(SkRegion::Op op) {
     switch (op) {
         case SkRegion::kUnion_Op: