Remove unnecessary crashpad:: qualification from implicit_cast<>

Remove unnecessary crashpad:: qualification from implicit_cast<>

This undoes 595803e1be18, a workaround that should no longer be
necessary now that base no longer provides implicit_cast<> in the global
namespace.

R=scottmg@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/9b9e49d0d9836d91420e1d4a3e5648432f10318d

[Mark Mentovai, 2015-09-17 16:31:56]

mark@chromium.org changed reviewers:
+ danakj@chromium.org

[Mark Mentovai, 2015-09-17 16:31:57]

Since https://codereview.chromium.org/1340683002/ stuck in Chrome and
https://codereview.chromium.org/1347483002/ did the same thing in mini_chromium,
this workaround shouldn’t be necessary any longer.

[scottmg, 2015-09-17 17:06:59]

scottmg@chromium.org changed reviewers:
+ scottmg@chromium.org

[scottmg, 2015-09-17 17:07:00]

lgtm

[Mark Mentovai, 2015-09-17 17:11:30]

Committed patchset #1 (id:1) manually as
9b9e49d0d9836d91420e1d4a3e5648432f10318d (presubmit successful).

[danakj, 2015-09-17 17:34:45]

Thanks :) LGTM