Fix one implicit 64-bit -> 32-bit implicit conversion in a PPAPI test.

../../ppapi/tests/test_url_loader.cc:877:11: warning: implicit conversion loses integer precision: 'int64_t' (aka 'long long') to 'int32_t' (aka 'int') [-Wshorten-64-to-32]
          total_bytes_to_be_received);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~

BUG=879657

Change-Id: I152f456368131fe7a2891ff0c97bf83f26ef0906
Reviewed-on: https://chromium-review.googlesource.com/c/1220173
Commit-Queue: Raymes Khoury <raymes@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600182}
TestURLLoader::TestURLLoader(TestingInstance* instance)
    : TestCase(instance),
      file_io_private_interface_(NULL),
      url_loader_trusted_interface_(NULL) {
}

TestURLLoader::TestURLLoader(TestingInstance* instance)
    : TestCase(instance),
      file_io_private_interface_(NULL),
      url_loader_trusted_interface_(NULL) {
}
