Make deployment of "icudtl.dat" optional

This is required to be done before chrome is using system's icu
because at that time the build of chrome will not generate icudtl.dat
on ChromeOS. For more discussion, please see,

https://docs.google.com/document/d/1T0H6DaRD9116pfaQMpBwfJtxlHPVJrroVsT_-SrAr1A/edit?usp=sharing

After libicu is installed, we should remove this line.

BUG=chromium:1020393
TEST=none

Change-Id: I706e86717f9ca15aca6f8b76c6929dc6755005ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2018402
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Tested-by: Honglin Yu <honglinyu@chromium.org>
Commit-Queue: Honglin Yu <honglinyu@chromium.org>
diff --git a/lib/chrome_util.py b/lib/chrome_util.py
index 608ed99..9df72c0 100644
--- a/lib/chrome_util.py
+++ b/lib/chrome_util.py
@@ -318,7 +318,8 @@
 
 # Files shared between all deployment types.
 _COPY_PATHS_COMMON = (
-    Path('icudtl.dat'),
+    # TODO(honglinyu): remove copying "icudtl.dat" after libicu is installed.
+    Path('icudtl.dat', optional=True),
     Path('libosmesa.so', exe=True, optional=True),
     # Do not strip the nacl_helper_bootstrap binary because the binutils
     # objcopy/strip mangles the ELF program headers.