Initial picture shader implementation

include/core/SkShader.h

Index: include/core/SkShader.h
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index acff959949ba5114bf2393dd4c0c181b376ab0b5..076ecf5460df9698021913279f6d13f5e3280179 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -16,6 +16,7 @@
 #include "SkPaint.h"
 
 class SkPath;
+class SkPicture;
 class GrContext;
 class GrEffectRef;
 
@@ -345,6 +346,16 @@ public:
     static SkShader* CreateBitmapShader(const SkBitmap& src,
                                         TileMode tmx, TileMode tmy);
 
+    /** Call this to create a new shader that will draw with the specified picture.
+     *
+     *  @param src  The picture to use inside the shader (if not NULL, its ref count

[scroggo, 2014/04/11 15:23:15]

Is it part of the intended use case to allow the caller to continue to modify
the picture? I'm looking at this with an eye towards immutability of shaders. If
we don't want the client to be able to modify it, we could make this take
ownership of the picture instead of reffing it. (And when we split the picture
API into picture record and picture playback, this could take a playback.)

[f(malita), 2014/04/11 16:05:18]

The intent is to treat the picture (playback) as immutable. If we can adjust the
API to better reflect this, SGTM.

+     *              is incremented).
+     *  @param tmx  The tiling mode to use when sampling the bitmap in the x-direction.
+     *  @param tmy  The tiling mode to use when sampling the bitmap in the y-direction.
+     *  @return     Returns a new shader object. Note: this function never returns null.
+    */
+    static SkShader* CreatePictureShader(SkPicture* src, TileMode tmx, TileMode tmy);
+
     SK_TO_STRING_VIRT()
     SK_DEFINE_FLATTENABLE_TYPE(SkShader)