Linux: fix build with system icu.

build/linux/unbundle/icu.gyp

Index: build/linux/unbundle/icu.gyp
diff --git a/build/linux/unbundle/icu.gyp b/build/linux/unbundle/icu.gyp
index 566df654fab42b4827b8e64e7eee8c93a0ca86e9..03f0ad4744c848557229aaa2d85a240bc3ad76fc 100644
--- a/build/linux/unbundle/icu.gyp
+++ b/build/linux/unbundle/icu.gyp
@@ -33,7 +33,7 @@
       'dependencies': ['system_icu'],
       'export_dependent_settings': ['system_icu'],
       'variables': {
-        'headers_root_path': 'public/i18n',
+        'headers_root_path': 'source/i18n',
         'header_filenames': [
           # This list can easily be updated using the command below:
           # find third_party/icu/source/i18n/unicode -iname '*.h' \
@@ -119,7 +119,7 @@
       'dependencies': ['system_icu'],
       'export_dependent_settings': ['system_icu'],
       'variables': {
-        'headers_root_path': 'public/common',
+        'headers_root_path': 'source/common',
         'header_filenames': [
           # This list can easily be updated using the command below:
           # find third_party/icu/source/common/unicode -iname '*.h' \