Update documentation around drawBitmap and shaders

include/core/SkShader.h

Index: include/core/SkShader.h
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index 11956ce0d2d187f8401b5224b7e12cd3cc80345e..cdb7a2fdbf64d4e9ef7428396f871e5f58e2c567 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -334,6 +334,9 @@ public:
      *  exceed implementation limits (currently at 64K - 1)) then SkEmptyShader
      *  may be returned.
      *
+     *  If the src is kA8_Config then that mask will be colorized using the color on
+     *  the paint.
+     *
      *  @param src  The bitmap to use inside the shader
      *  @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.