Fix gcc 4.9 build errors.

runtime/bin/main.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_tools_api.h"
@@ skipping 1399 matching lines @@
     }
 
     if (gen_precompiled_snapshot) {
       uint8_t* vm_isolate_buffer = NULL;
       intptr_t vm_isolate_size = 0;
       uint8_t* isolate_buffer = NULL;
       intptr_t isolate_size = 0;
       uint8_t* assembly_buffer = NULL;
       intptr_t assembly_size = 0;
       uint8_t* instructions_blob_buffer = NULL;
-      intptr_t instructions_blob_size = NULL;
+      intptr_t instructions_blob_size = 0;
       uint8_t* rodata_blob_buffer = NULL;
-      intptr_t rodata_blob_size = NULL;
+      intptr_t rodata_blob_size = 0;
       if (use_blobs) {
         result = Dart_CreatePrecompiledSnapshotBlob(
             &vm_isolate_buffer,
             &vm_isolate_size,
             &isolate_buffer,
             &isolate_size,
             &instructions_blob_buffer,
             &instructions_blob_size,
             &rodata_blob_buffer,
             &rodata_blob_size);
@@ skipping 354 matching lines @@
   Platform::Exit(Process::GlobalExitCode());
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   dart::bin::main(argc, argv);
   UNREACHABLE();
 }