Remove NavigationRequestInfo::is_showing.

Remove NavigationRequestInfo::is_showing.

Trying to initialize it causes content_shell --enable-browser-side-navigation
to crash on startup.

It corresponds to ResourceRequestInfo::GetVisibilityState, but that's only used
for categorizing requests made from prerender which needs a different bit
(WebPageVisiblityStatePrerender vs. others), so we'll need to revisit it
anyway.

BUG=376014
Committed: https://crrev.com/90147459e59132fea1c6254e9d30478735ec7247
Cr-Commit-Position: refs/heads/master@{#293211}

[davidben, 2014-09-03 18:41:38]

davidben@chromium.org changed reviewers:
+ clamy@chromium.org, nasko@chromium.org

[davidben, 2014-09-03 18:41:38]

May as well split this out of the rest of the RDH stuff since it's pretty tiny
and self-contained.

[nasko, 2014-09-03 18:46:22]

LGTM

[clamy, 2014-09-03 18:49:54]

lgtm

[davidben, 2014-09-03 18:53:20]

The CQ bit was checked by davidben@chromium.org

[commit-bot: I haz the power, 2014-09-03 18:53:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/davidben@chromium.org/534393002/1

[commit-bot: I haz the power, 2014-09-03 19:57:52]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[commit-bot: I haz the power, 2014-09-03 23:15:59]

Committed patchset #1 (id:1) as 142a78b5c6f45b0892f24f66ee1be60e727bd78c

[commit-bot: I haz the power, 2014-09-10 03:28:14]

Patchset 1 (id:??) landed as
https://crrev.com/90147459e59132fea1c6254e9d30478735ec7247
Cr-Commit-Position: refs/heads/master@{#293211}