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

include/core/SkCanvas.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 426 matching lines @@
 
     /** Replace the current matrix with a copy of the specified matrix.
         @param matrix The matrix that will be copied into the current matrix.
     */
     void setMatrix(const SkMatrix& matrix);
 
     /** Helper for setMatrix(identity). Sets the current matrix to identity.
     */
     void resetMatrix();
 
+    /** Set the current draw depth of the canvas.
+        @param z    The SkScalar depth; it's tracked in the save/restore stack.
+                    Negative into screen, positive out of screen.
+
+    */
+    void setZ(SkScalar z);

[jvanverth1, 2016/07/11 18:13:43]

Based on today's discussion, this should be changed to translateZ, and its
behavior changed to be relative to any previous translateZs. I.e.,
translateZ(1.0) followed by translateZ(2.0) should end up with a translation of
3.0.

I wouldn't do that in this patch, but in a subsequent one. Just noting it for
later.

[vjiaoblack, 2016/07/11 18:58:03]

Acknowledged.

+
+    /** Returns the current draw depth of the canvas.
+    */
+    SkScalar getZ() const;
+
     /**
      *  Modify the current clip with the specified rectangle.
      *  @param rect The rect to combine with the current clip
      *  @param op The region op to apply to the current clip
      *  @param doAntiAlias true if the clip should be antialiased
      */
     void clipRect(const SkRect& rect,
                   SkRegion::Op op = SkRegion::kIntersect_Op,
                   bool doAntiAlias = false);
 
@@ skipping 843 matching lines @@
 
     virtual void willSave() {}
     // Overriders should call the corresponding INHERITED method up the inheritance chain.
     virtual SaveLayerStrategy getSaveLayerStrategy(const SaveLayerRec&) {
         return kFullLayer_SaveLayerStrategy;
     }
     virtual void willRestore() {}
     virtual void didRestore() {}
     virtual void didConcat(const SkMatrix&) {}
     virtual void didSetMatrix(const SkMatrix&) {}
+    virtual void didSetZ(SkScalar) {}
 
     virtual void onDrawAnnotation(const SkRect&, const char key[], SkData* value);
     virtual void onDrawDRRect(const SkRRect&, const SkRRect&, const SkPaint&);
 
     virtual void onDrawText(const void* text, size_t byteLength, SkScalar x,
                             SkScalar y, const SkPaint& paint);
 
     virtual void onDrawPosText(const void* text, size_t byteLength,
                                const SkPoint pos[], const SkPaint& paint);
 
@@ skipping 265 matching lines @@
 
 class SkCanvasClipVisitor {
 public:
     virtual ~SkCanvasClipVisitor();
     virtual void clipRect(const SkRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipRRect(const SkRRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipPath(const SkPath&, SkRegion::Op, bool antialias) = 0;
 };
 
 #endif