Documentation: C API comments

Review URL: https://codereview.chromium.org/1271023002
diff --git a/include/c/sk_surface.h b/include/c/sk_surface.h
index f3c17d0..d634185 100644
--- a/include/c/sk_surface.h
+++ b/include/c/sk_surface.h
@@ -15,10 +15,46 @@
 
 SK_C_PLUS_PLUS_BEGIN_GUARD
 
+/**
+    Return a new surface, with the memory for the pixels automatically
+    allocated.  If the requested surface cannot be created, or the
+    request is not a supported configuration, NULL will be returned.
+
+    @param sk_imageinfo_t* Specify the width, height, color type, and
+                           alpha type for the surface.
+
+    @param sk_surfaceprops_t* If not NULL, specify additional non-default
+                              properties of the surface.
+*/
 SK_API sk_surface_t* sk_surface_new_raster(const sk_imageinfo_t*, const sk_surfaceprops_t*);
+
+/**
+    Create a new surface which will draw into the specified pixels
+    with the specified rowbytes.  If the requested surface cannot be
+    created, or the request is not a supported configuration, NULL
+    will be returned.
+
+    @param sk_imageinfo_t* Specify the width, height, color type, and
+                           alpha type for the surface.
+    @param void* pixels Specify the location in memory where the
+                        destination pixels are.  This memory must
+                        outlast this surface.
+     @param size_t rowBytes Specify the difference, in bytes, between
+                           each adjacent row.  Should be at least
+                           (width * sizeof(one pixel)).
+    @param sk_surfaceprops_t* If not NULL, specify additional non-default
+                              properties of the surface.
+*/
 SK_API sk_surface_t* sk_surface_new_raster_direct(const sk_imageinfo_t*,
                                                   void* pixels, size_t rowBytes,
                                                   const sk_surfaceprops_t* props);
+
+/**
+    Decrement the reference count. If the reference count is 1 before
+    the decrement, then release both the memory holding the
+    sk_surface_t and any pixel memory it may be managing.  New
+    sk_surface_t are created with a reference count of 1.
+*/
 SK_API void sk_surface_unref(sk_surface_t*);
 
 /**