Looks like we should add x11-utils to the list of required ubuntu packages.

After I did this:

* create a chroot environment for trusty
* install git
* clone depot_tools
* fetch --nohooks chromium
* sudo ./build/install-build-deps.sh
* gclient runhooks
* gn gen out/Default
* ninja -C out/Default blink_tests

Then I got this:

```
(chromium)jwolfe@jwolfe-desktop:~/chromium/src$ python third_party/WebKit/Tools/Scripts/run-webkit-tests -t Default
Using port 'linux-trusty'
Test configuration: <trusty, x86_64, debug>
View the test results at file:///home/jwolfe/chromium/src/out/Default/layout-test-results/results.html
Using random order with seed: 1501089613
Baseline search path: linux -> win -> generic
Using Debug build
Pixel tests enabled
Regular timeout: 18000, slow test timeout: 90000
Command line: /home/jwolfe/chromium/src/out/Default/content_shell --run-layout-test --ignore-certificate-errors-spki-list=Nxvaj3+bY3oVrTc+Jp7m3E3sB1n3lXtnMDCyBsqEXiY= --enable-crash-reporter --crash-dumps-dir=/home/jwolfe/chromium/src/out/Default/crash-dumps -

Found 68490 tests; running 59617, skipping 8873.   
Checking build ...
OSError raised: [Errno 2] No such file or directory
Traceback (most recent call last):
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py", line 67, in main
    return run(port, options, args, stderr, stdout).exit_code
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py", line 597, in run
    run_details = _run_tests(port, options, args, printer)
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py", line 588, in _run_tests
    return manager.run(args)
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager.py", line 141, in run
    exit_code = self._set_up_run(tests_to_run)
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager.py", line 349, in _set_up_run
    self._port.setup_test_run()
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux.py", line 112, in setup_test_run
    self._start_xvfb()
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux.py", line 153, in _start_xvfb
    display = self._find_display()
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux.py", line 208, in _find_display
    ['xdpyinfo', '-display', display], return_exit_code=True)
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive.py", line 309, in run_command
    close_fds=self._should_close_fds())
  File "/home/jwolfe/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive.py", line 377, in popen
    return subprocess.Popen(string_args, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1327, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory
```