Make readpixels work on GrTextures

src/gpu/GrSurfacePriv.h

Index: src/gpu/GrSurfacePriv.h
diff --git a/src/gpu/GrSurfacePriv.h b/src/gpu/GrSurfacePriv.h
index 47bd44f4ef1ba00d5ec12bbe3fff974da582e60c..bff411edf3e0089d504daf9135a4b81592a0ef08 100644
--- a/src/gpu/GrSurfacePriv.h
+++ b/src/gpu/GrSurfacePriv.h
@@ -17,6 +17,21 @@
     implemented privately in GrSurface with a inline public method here). */
 class GrSurfacePriv {
 public:
+    /** Helpers used in read/write pixels implementations. The paramters are adjusted so that the
+        read/write respects the bounds of a surface. If the input *rowBytes is 0 it will be
+        the tight row bytes (based on width and bpp) on output. */
+    static bool AdjustReadPixelParams(int surfaceWidth,
+                                      int surfaceHeight,
+                                      size_t bpp,
+                                      int* left, int* top, int* width, int* height,
+                                      void** data,
+                                      size_t* rowBytes);
+    static bool AdjustWritePixelParams(int surfaceWidth,
+                                      int surfaceHeight,
+                                      size_t bpp,
+                                      int* left, int* top, int* width, int* height,
+                                      const void** data,
+                                      size_t* rowBytes);
     /**
      * Derive a SkImageInfo from the surface's descriptor. The caller must provide the alpha type as
      * GrSurface has no equivalent.