Provide Better Error Messages when isolated is missing a dll

Repro:
1. Add a dependency to a new dll to a isolate target
2. Try and run the target in isolate

Expected:
Isolate tells me that it failed to load a dependency and suggests I need to 
update my isolate files.

Actual:
Isolate gives me a strange exit code and I don't have any idea what is going 
on. 

E:\b\build\slave\win\build>call python 
E:\b\build\scripts\slave\..\command_wrapper\bin\command_wrapper.py -- python 
E:\b\build\scripts\slave\..\..\third_party\gsutil\gsutil cp 
file://c:\users\chrome~2\appdata\local\temp\tmprj3jti 
gs://chrome-gtest-results/2014/2/10/12/aaf74ffa0dcadaccf685f2bbe7fc3dc337d990c7.
json.gz 
Copying file://c:\users\chrome~2\appdata\local\temp\tmprj3jti 
[Content-Type=application/octet-stream]...
exit code (as seen by runtest.py): -1073741515

In my case, I hadn't realized that my change had added a new dll dependency to 
unit_tests.exe and interactive_ui_tests.exe and was even more confused since 
browser_tests.exe didn't show the same problem (since it included 
chrome.isolate which included chrome_elf.dll).

Original issue reported on code.google.com by csharp@chromium.org on 12 Feb 2014 at 4:36

madecoste / swarming

Provide Better Error Messages when isolated is missing a dll #76