UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36

Steps to reproduce the problem:
create Dockerfile with content:

```
FROM ubuntu:latest

RUN apt-get update && apt-get -y install git \
                                         pkg-config \
                                         python
WORKDIR /root
RUN git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
ENV PATH "$PATH:/root/depot_tools"
RUN fetch v8
RUN gclient sync -r 4.10.253
CMD bash
```

What is the expected behavior?
gclient sync -r 4.10.253 should finished successfully

What went wrong?
v8/buildtools (ERROR)                                                                                                                                                
----------------------------------------                                                                                                                             
[0:00:16] Started.                                                                                                                                                   
_____ v8/buildtools at ef3e530703353ba8ad094694ba7c156daddbddeb                                                                                                      
----------------------------------------                                                                                                                             
Traceback (most recent call last):                                                                                                                                   
  File "/root/depot_tools/gclient.py", line 2295, in <module>                                                                                                        
    sys.exit(main(sys.argv[1:]))                                                                                                                                     
  File "/root/depot_tools/gclient.py", line 2281, in main                                                                                                            
    return dispatcher.execute(OptionParser(), argv)                                                                                                                  
  File "/root/depot_tools/subcommand.py", line 252, in execute                                                                                                       
    return command(parser, args[1:])                                                                                                                                 
  File "/root/depot_tools/gclient.py", line 2030, in CMDsync                                                                                                         
    ret = client.RunOnDeps('update', args)                                                                                                                           
  File "/root/depot_tools/gclient.py", line 1340, in RunOnDeps                                                                                                       
    work_queue.flush(revision_overrides, command, args, options=self._options)                                                                                       
  File "/root/depot_tools/gclient_utils.py", line 1047, in run                                                                                                       
    self.item.run(*self.args, **self.kwargs)                                                                                                                         
  File "/root/depot_tools/gclient.py", line 766, in run                                                                                                              
    self.ParseDepsFile()                                                                                                                                             
  File "/root/depot_tools/gclient.py", line 562, in ParseDepsFile                                                                                                    
    gclient_eval.Check(deps_content, filepath, global_scope, local_scope)                                                                                            
  File "/root/depot_tools/gclient_eval.py", line 236, in Check                                                                                                       
    result_scope = _gclient_exec(content, global_scope, filename=path)                                                                                               
  File "/root/depot_tools/gclient_eval.py", line 181, in _gclient_exec
    _visit_in_module(stmt)
  File "/root/depot_tools/gclient_eval.py", line 165, in _visit_in_module
    value = _gclient_eval(node.value, global_scope, filename=filename)
  File "/root/depot_tools/gclient_eval.py", line 142, in _gclient_eval
    return _convert(node_or_string)
  File "/root/depot_tools/gclient_eval.py", line 141, in _convert
    getattr(node, 'lineno', '<unknown>')))
ValueError: unexpected AST node: <_ast.Num object at 0x7f0c416d7950> Num(n=1) (file '/root/v8/buildtools/DEPS', line 1)

Did this work before? N/A 

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