x11: Use scoped_ptr<> for X11 objects where it makes sense.

x11: Use scoped_ptr<> for X11 objects where it makes sense.

Introduce gfx::XScopedPtr<> as a convenience wrapper around scoped_ptr<>
for managing X11 objects. The return types of the X11 deleter functions are
somewhat inconsistent (e.g. XFree returns int, whereas XIFreeDeviceInfo
doesn't return anything), which makes this a bit tricky. So introduce a
custom deleter gfx::XObjectDeleter to use with XScopedPtr<>. Using this
XScopedPtr<> allows for cleaner code in a few places, and should generally
make it easier to manage X11 objects.

Additional clean-ups:
. content/common/gpu/x_util.cc is unused. So remove that.
. ui::XScopedString is unused. So remove that.
. DeviceListCacheX11 has support for maintaining the device-list cache for
  multiple X11 connections, but chrome doesn't have support for more than
  one. So replace the map with a single cache. (necessitated by the use of
  XScopedPtr<> in DeviceList.)

BUG=none
R=piman@chromium.org, sky@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/c351e9566c24e050a57671bee6beeaad1771ab84

[sadrul, 2015-03-08 07:42:01]

sadrul@chromium.org changed reviewers:
+ piman@chromium.org, sky@chromium.org

[sadrul, 2015-03-08 07:42:02]

sky@chromium.org: Please review changes in ash/ chrome/ and ui/

piman@chromium.org: Please review changes in content/

[sky, 2015-03-09 15:44:49]

LGTM

[piman, 2015-03-09 22:33:05]

LGTM, nice cleanup

[commit-bot: I haz the power, 2015-03-10 01:36:30]

Patchset 5 (id:??) landed as
https://crrev.com/c351e9566c24e050a57671bee6beeaad1771ab84
Cr-Commit-Position: refs/heads/master@{#319809}

[sadrul, 2015-03-10 01:47:56]

Committed patchset #5 (id:70001) manually as
c351e9566c24e050a57671bee6beeaad1771ab84 (presubmit successful).