Optimize RTL check in ICU to avoid mmap access.

base/i18n/rtl.cc

Index: base/i18n/rtl.cc
diff --git a/base/i18n/rtl.cc b/base/i18n/rtl.cc
index 96ef9aaecd257b16b9e8054e90c5421776a5e8c8..efa155ea2b666157966738467f3812aa20759e95 100644
--- a/base/i18n/rtl.cc
+++ b/base/i18n/rtl.cc
@@ -6,7 +6,6 @@
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
-#include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
@@ -126,21 +125,28 @@ bool IsRTL() {
 bool ICUIsRTL() {
   if (g_icu_text_direction == UNKNOWN_DIRECTION) {
     const icu::Locale& locale = icu::Locale::getDefault();
-    g_icu_text_direction = GetTextDirectionForLocale(locale.getName());
+    g_icu_text_direction = GetTextDirectionForLocaleInStartUp(locale.getName());
   }
   return g_icu_text_direction == RIGHT_TO_LEFT;
 }
 
-TextDirection GetTextDirectionForLocale(const char* locale_name) {
-  const std::string group_name =
-      FieldTrialList::FindFullName("LightSpeed");
-  // StartsWith allows flexibility for this experiment to apply to multiple
-  // group names. To start, this will apply to AvoidMMapOnStartup.
-  if (StartsWith(group_name, "AvoidMMap", CompareCase::SENSITIVE)) {
-    static const char kEnglishLocale[] = "en_";
-    if (StartsWith(locale_name, kEnglishLocale, CompareCase::SENSITIVE))
-      return LEFT_TO_RIGHT;
+TextDirection GetTextDirectionForLocaleInStartUp(const char* locale_name) {
+  // This list needs to be updated if we add more RTL locales.
+  static const char* kRTLLocales[] = {
+    "ar",
+    "fa",
+    "he",
+    "iw",
+    "ur"
+  };
+  for (const char* rtl_locale : kRTLLocales) {
+    if (StartsWith(locale_name, rtl_locale, CompareCase::SENSITIVE))

[jungshik at Google, 2015/08/11 20:38:29]

One more thing I forgot to mention. Sorry that I didn't mention it in the first
round. 

Instead of StartsWith, you have to get the language code (chopping |locale_name|
at the 1st '_' or '-')  and compare the result against the list. That way, you
can defend against a case where 3-letter language code (for some languages,
there's no 2-letter code and we have to use 3-letter codes) happens to starts
with one of the above. 

[jungshik at Google, 2015/08/11 20:41:59]

Because the only 3-letter language code in the current list of Chrome's UI
languages is 'fil' and it's not a prefix match for any of the above. So, it's
theoeretical.  So, if you really think it can affect perf, you can comment this
and use StartsWith, but I guess perf impact would be really tiny if you do the
right thing. 

[danduong, 2015/08/11 21:03:16]

That was definitely an oversight on my part. Thanks for the catch!

+      return RIGHT_TO_LEFT;
   }
+  return LEFT_TO_RIGHT;
+}
+
+TextDirection GetTextDirectionForLocale(const char* locale_name) {
   UErrorCode status = U_ZERO_ERROR;
   ULayoutType layout_dir = uloc_getCharacterOrientation(locale_name, &status);
   DCHECK(U_SUCCESS(status));