Add SkData::NewFromFD.

include/core/SkOSFile.h

Index: include/core/SkOSFile.h
===================================================================
--- include/core/SkOSFile.h	(revision 9384)
+++ include/core/SkOSFile.h	(working copy)
@@ -54,10 +54,17 @@
 
 /** Maps a file into memory. Returns the address and length on success, NULL otherwise.
  *  The mapping is read only.
+ *  When finished with the mapping, free the returned pointer with sk_fmunmap.
  */
 void*   sk_fmmap(SkFILE* f, size_t* length);
 
-/** Unmaps a file previously mapped by sk_fmmap.
+/** Maps a file descriptor into memory. Returns the address and length on success, NULL otherwise.
+ *  The mapping is read only.
+ *  When finished with the mapping, free the returned pointer with sk_fmunmap.
+ */
+void*   sk_fdmmap(int fd, size_t* length);
+
+/** Unmaps a file previously mapped by sk_fmmap or sk_fdmmap.
  *  The length parameter must be the same as returned from sk_fmmap.
  */
 void    sk_fmunmap(const void* addr, size_t length);
@@ -65,6 +72,11 @@
 /** Returns true if the two point at the exact same filesystem object. */
 bool    sk_fidentical(SkFILE* a, SkFILE* b);
 
+/** Returns the underlying file descriptor for the given file.
+ *  The return value will be < 0 on failure.
+ */
+int     sk_fileno(SkFILE* f);
+
 // Returns true if something (file, directory, ???) exists at this path.
 bool    sk_exists(const char *path);