Remove trailing backslash in comment causing multiline comment warning.

Remove trailing backslash in comment causing multiline comment warning on chromeos_amd64.

BUG=514575
TBR=pneubeck@chromium.org, benwells@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/4c18992a34fdd4c7a5e33d30e55a59c4aec03ebf

[engedy, 2015-09-09 14:15:17]

engedy@chromium.org changed reviewers:
+ benwells@chromium.org, pneubeck@chromium.org

[engedy, 2015-09-09 14:17:34]

This caused on issue on trybots, e.g.:
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromeos_amd64-...

[1226/1227] CXX
obj/chrome/browser/extensions/api/certificate_provider/browser_tests.certificate_provider_apitest.o
FAILED:
obj/chrome/browser/extensions/api/certificate_provider/browser_tests.certificate_provider_apitest.o
../../chrome/browser/extensions/api/certificate_provider/certificate_provider_apitest.cc:246:5:error:
multi-line comment [-Werror=comment]
     // openssl x509 -inform DER -noout -fingerprint -in \
     ^
cc1plus.elf: all warnings being treated as errors
ninja: build stopped: subcommand failed.

[engedy, 2015-09-09 14:19:53]

Committed patchset #1 (id:1) manually as
4c18992a34fdd4c7a5e33d30e55a59c4aec03ebf (presubmit successful).

[pneubeck (no reviews), 2015-09-09 14:23:19]

lgtm

[engedy, 2015-09-09 14:26:44]

On 2015/09/09 14:23:19, pneubeck wrote:
> lgtm

Please feel free to adjust the comment format as you see fit, we just didn't
want to overthink how to do it, but wanted to make the trybots green ASAP.