Add a src rect to drawImageLattice() API

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index 7bf84c978fed4aa0d549c4c29ab94b3f19084aa6..6251917301ae4725909d0985b559995cba642153 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -964,20 +964,20 @@ public:
         };
 
         // An array of x-coordinates that divide the bitmap vertically.
-        // These must be unique, increasing, and in the set [0, width).
+        // These must be unique, increasing, and in the set [fBounds.fLeft, fBounds.fRight).
         // Does not have ownership.
         const int*   fXDivs;
 
         // An array of y-coordinates that divide the bitmap horizontally.
-        // These must be unique, increasing, and in the set [0, height).
+        // These must be unique, increasing, and in the set [fBounds.fTop, fBounds.fBottom).
         // Does not have ownership.
         const int*   fYDivs;
 
         // If non-null, the length of this array must be equal to
         // (fXCount + 1) * (fYCount + 1).  Note that we allow the first rect
-        // in each direction to empty (divs[0] = 0).  In this case, the
-        // caller still must specify a flag (as a placeholder) for these
-        // empty rects.
+        // in each direction to be empty (ex: fXDivs[0] = fBounds.fLeft).
+        // In this case, the caller still must specify a flag (as a placeholder)
+        // for these empty rects.
         // The flags correspond to the rects in the lattice, first moving
         // left to right and then top to bottom.
         const Flags* fFlags;
@@ -987,6 +987,10 @@ public:
 
         // The number of fYDivs.
         int          fYCount;
+
+        // The bound to draw from.  Will ofetn be equal to the bounds of the
+        // input SkImage.

[reed1, 2016/09/29 21:11:38]

1. could take a ptr to a rect, and null means the entire src (just a thought,
matches some of our other calls)
2. what is our behavior defined to be if fBounds extends beyond the image
dimensions? is empty or inverted?

+        SkIRect      fBounds;
     };
 
     /**