mb run failing with JSON error

[Fergal Daly]

I'm trying to run a test in the cloud and the following command is failing with

```

tools/mb/mb run --no-build -s --no-default-dimensions -d pool chromium.tests -d cpu x86-64 out/linux-opt content_browsertests

...

: invalid character '.' after array element
  -> returned 1

```

The "..." there is a huge chunk of JSON that parses just fine with eval() in python.

I haven't run mb for some time, so I don't know when this started happening,

F

[Fergal Daly]

I've filed https://crbug.com/1280069 for this,

F