[intl] Remove redundant flattening of strings.

Patch from Chukwuchebem Orakwue <c.orakwue@samsung.com>

Change-Id: Ic5b302f4965b0f032839ef06e1221f56c37f76a1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1582055Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61341}

src/objects/intl-objects.cc

@@ -193,15 +193,13 @@ const uint8_t* Intl::ToLatin1LowerTable() { return &kToLower[0]; }
 
 icu::UnicodeString Intl::ToICUUnicodeString(Isolate* isolate,
                                             Handle<String> string) {
-  string = String::Flatten(isolate, string);
-  {
-    DisallowHeapAllocation no_gc;
-    std::unique_ptr<uc16[]> sap;
-    return icu::UnicodeString(
-        GetUCharBufferFromFlat(string->GetFlatContent(no_gc), &sap,
-                               string->length()),
-        string->length());
-  }
+  DCHECK(string->IsFlat());
+  DisallowHeapAllocation no_gc;
+  std::unique_ptr<uc16[]> sap;
+  return icu::UnicodeString(
+      GetUCharBufferFromFlat(string->GetFlatContent(no_gc), &sap,
+                             string->length()),
+      string->length());
 }
 
 namespace {
@@ -1671,6 +1669,7 @@ Intl::ResolvedLocale Intl::ResolveLocale(
 
 Managed<icu::UnicodeString> Intl::SetTextToBreakIterator(
     Isolate* isolate, Handle<String> text, icu::BreakIterator* break_iterator) {
+  text = String::Flatten(isolate, text);
   icu::UnicodeString* u_text =
       (icu::UnicodeString*)(Intl::ToICUUnicodeString(isolate, text).clone());
 

src/objects/js-list-format.cc

@@ -286,8 +286,9 @@ Maybe<std::vector<icu::UnicodeString>> ToUnicodeStringArray(
                        factory->NewNumber(i), factory->String_string()),
           Nothing<std::vector<icu::UnicodeString>>());
     }
-    result.push_back(
-        Intl::ToICUUnicodeString(isolate, Handle<String>::cast(item)));
+    Handle<String> item_str = Handle<String>::cast(item);
+    if (!item_str->IsFlat()) item_str = String::Flatten(isolate, item_str);
+    result.push_back(Intl::ToICUUnicodeString(isolate, item_str));
   }
   DCHECK(!array->HasDictionaryElements());
   return Just(result);

test/intl/list-format/format.js

@@ -41,6 +41,10 @@ function testFormatter(listFormat) {
   assertThrows(() => listFormat.format([null, 'world']), TypeError);
   assertThrows(() => listFormat.format(['hello', null]), TypeError);
   assertThrows(() => listFormat.format([null]), TypeError);
+
+  // Test that Cons strings are handled correctly.
+  let arr = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m"];
+  assertListFormat(listFormat, [arr + "n"]);
 }
 testFormatter(new Intl.ListFormat());
 testFormatter(new Intl.ListFormat(["en"]));