Correct attribute name in IsInForcedRTL()

AppleTextDirection is set for all RTL languages, whereas
NSForceRightToLeftWritingDirection is only set for the RTL psuedolanguage.

BUG= 534358

Review URL: https://codereview.chromium.org/1356073002

Cr-Commit-Position: refs/heads/master@{#349948}

base/ios/ios_util.h

@@ -21,7 +21,10 @@ BASE_EXPORT bool IsRunningOnIOS9OrLater();
 BASE_EXPORT bool IsRunningOnOrLater(int32 major, int32 minor, int32 bug_fix);
 
 // Returns whether iOS is signalling that an RTL text direction should be used
-// regardless of the current locale.
+// regardless of the current locale. This should not return true if the current
+// language is a "real" RTL language such as Arabic or Urdu; it should only
+// return true in cases where the RTL text direction has been forced (for
+// example by using the "RTL Psuedolanguage" option when launching from XCode).
 BASE_EXPORT bool IsInForcedRTL();
 
 }  // namespace ios

base/ios/ios_util.mm

@@ -43,7 +43,7 @@ bool IsRunningOnOrLater(int32 major, int32 minor, int32 bug_fix) {
 
 bool IsInForcedRTL() {
   NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
-  return [defaults boolForKey:@"AppleTextDirection"];
+  return [defaults boolForKey:@"NSForceRightToLeftWritingDirection"];
 }
 
 }  // namespace ios