Turn on icu_use_data_file_flag on CrOS

Turn on icu_use_data_file_flag on CrOS

See also https://chromium-review.googlesource.com/#/c/185937/

The switch has to be turned on in two places (chromeos-chrome.ebuild and
build/common.gypi). One or the other can get landed separately, though.

Note to perf sheriff : chrome (executable) will get smaller by 10MB, but the chrome os image size will not change because what used to be statically linked (icudtl.dat) is now in a separate file in the same location.

BUG=72633
TEST=net_unittests:*IDN* and base_unittests:*String*
TBR=mark

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251213

[jungshik at Google, 2014-02-13 21:45:37]

The CQ bit was checked by jshin@chromium.org

[commit-bot: I haz the power, 2014-02-13 21:49:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jshin@chromium.org/163793004/20001

[commit-bot: I haz the power, 2014-02-14 00:48:13]

Change committed as 251213

[jungshik at Google, 2014-02-14 00:55:15]

A revert of this CL has been created in
https://codereview.chromium.org/165593002/ by jshin@chromium.org.

The reason for reverting is:
https://chromium-review.googlesource.com/#/c/185937/ has to go in first. 
.