Fix startup with system ICU

We need to configure code to use built-in data from system library,
not a separate file shipped with Chrome.

BUG=551343
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/2339173005 .

Cr-Commit-Position: refs/heads/master@{#418989}

build/linux/unbundle/icu.gn

@@ -13,7 +13,10 @@ group("icu") {
 }
 
 config("icu_config") {
-  defines = [ "USING_SYSTEM_ICU=1" ]
+  defines = [
+    "USING_SYSTEM_ICU=1",
+    "ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_STATIC",
+  ]
 }
 
 pkg_config("system_icui18n") {