Roll ICU to 297a4dd02b

For actual changes, see

  https://chromium-review.googlesource.com/1145582

TBR=manojgupta@chromium.org
BUG=chromium:865100
TEST=locally built chrome os image works.

Change-Id: Ifeaa0092937977fbb942741b1f348845c1e4596f
Reviewed-on: https://chromium-review.googlesource.com/1147108Reviewed-by: Jungshik Shin <jshin@chromium.org>
Reviewed-by: Jun Mukai <mukai@chromium.org>
Commit-Queue: Jungshik Shin <jshin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577267}

DEPS

@@ -705,7 +705,7 @@ deps = {
     Var('chromium_git') + '/chromium/deps/hunspell_dictionaries.git' + '@' + 'a9bac57ce6c9d390a52ebaad3259f5fdb871210e',
 
   'src/third_party/icu':
-    Var('chromium_git') + '/chromium/deps/icu.git' + '@' + 'a9a2bd3ee4f1d313651c5272252aaf2a3e7ed529',
+    Var('chromium_git') + '/chromium/deps/icu.git' + '@' + '297a4dd02b9d36c92ab9b4f121e433c9c3bc14f8',
 
   'src/third_party/icu4j': {
       'packages': [