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();
 
+    /** Change the current draw depth of the canvas with a translation.

[jvanverth1, 2016/07/13 13:54:24]

Suggestion: Add the specified translation to the current draw depth of the
canvas.
            @param z  The distance to translate in z.
                      Negative into screen, positive out of screen.

            Without translation, the draw depth defaults to 0.

[vjiaoblack, 2016/07/13 14:55:43]

Done.

+        @param z    The SkScalar depth; it's tracked in the save/restore stack.
+                    Negative into screen, positive out of screen.
+                    Defaults to 0.
+    */
+    void translateZ(SkScalar z);
+
     /**
      *  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 781 matching lines @@
                                const SkPaint* paint,
                                SrcRectConstraint constraint = kStrict_SrcRectConstraint);
 
     // expose minimum amount of information necessary for transitional refactoring
     /**
      * Returns CTM and clip bounds, translated from canvas coordinates to top layer coordinates.
      */
     void temporary_internal_describeTopLayer(SkMatrix* matrix, SkIRect* clip_bounds);
 
 protected:
+    /** Returns the current (cumulative) draw depth of the canvas.
+      */
+    SkScalar getZ() const;
+
     /** After calling saveLayer(), there can be any number of devices that make
         up the top-most drawing area. LayerIter can be used to iterate through
         those devices. Note that the iterator is only valid until the next API
         call made on the canvas. Ownership of all pointers in the iterator stays
         with the canvas, so none of them should be modified or deleted.
     */
     class LayerIter /*: SkNoncopyable*/ {
     public:
         /** Initialize iterator with canvas, and set values for 1st device */
         LayerIter(SkCanvas*, bool skipEmptyClips);
@@ skipping 42 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 didTranslateZ(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