Add a get_random_bytes() syscall to replace the SRPC-based implementation

src/shared/platform/nacl_global_secure_random.c

 /*
  * Copyright (c) 2011 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * NaCl Service Runtime.  Secure RNG abstraction.
  */
 
@@ skipping 37 matching lines @@
 }
 
 uint32_t NaClGlobalSecureRngUint32(void) {
   uint32_t rv;
   NaClXMutexLock(&nacl_global_rng_mu);
   rv = (*nacl_grngp->base.vtbl->GenUint32)(&nacl_grngp->base);
   NaClXMutexUnlock(&nacl_global_rng_mu);
   return rv;
 }
 
+void NaClGlobalSecureRngGenerateBytes(uint8_t *buf, size_t buf_size) {
+  NaClXMutexLock(&nacl_global_rng_mu);
+  (*nacl_grngp->base.vtbl->GenBytes)(&nacl_grngp->base, buf, buf_size);
+  NaClXMutexUnlock(&nacl_global_rng_mu);
+}
+
 void NaClGenerateRandomPath(char *path, int length) {
   /*
    * This function is used for generating random paths and names,
    * e.g. for IMC sockets and semaphores.
    *
    * IMC sockets note: the IMC header file omits some important
    * details.  The alphabet cannot include backslash for Windows.  For
    * Linux, it uses the abstract namespace (see unix(7)), and can
    * contain arbitrary characters.  The limitations for OSX are the
    * same as for pathname components, since the IMC library uses
@@ skipping 49 matching lines @@
 
   int               i;
   int               r;
 
   for (i = 0; i < length-1; ++i) {
     r = NaClGlobalSecureRngUniform(alphabet_size);
     path[i] = alphabet[r];
   }
   path[length-1] = '\0';
 }