Add CodeStubAssembler::FlattenString

test/cctest/test-code-stub-assembler.cc

Index: test/cctest/test-code-stub-assembler.cc
diff --git a/test/cctest/test-code-stub-assembler.cc b/test/cctest/test-code-stub-assembler.cc
index c83af5860543fd9ab277390329688966260e2040..d55c82e8eac28bcdb761c714f59db24f9823b5d1 100644
--- a/test/cctest/test-code-stub-assembler.cc
+++ b/test/cctest/test-code-stub-assembler.cc
@@ -175,6 +175,46 @@ TEST(ToString) {
   }
 }
 
+TEST(FlattenString) {
+  Isolate* isolate(CcTest::InitIsolateOnce());
+  const int kNumParams = 1;
+  CodeStubAssemblerTester m(isolate, kNumParams);
+  m.Return(m.FlattenString(m.Parameter(0)));
+
+  Handle<Code> code = m.GenerateCode();
+  FunctionTester ft(code, kNumParams);
+
+  Handle<FixedArray> test_cases(isolate->factory()->NewFixedArray(4));
+  Handle<String> expected(
+      isolate->factory()->InternalizeUtf8String("hello, world!"));
+  test_cases->set(0, *expected);
+
+  Handle<String> string(
+      isolate->factory()->InternalizeUtf8String("filler hello, world! filler"));
+  Handle<String> sub_string(
+      isolate->factory()->NewProperSubString(string, 7, 20));
+  test_cases->set(1, *sub_string);
+
+  Handle<String> hello(isolate->factory()->InternalizeUtf8String("hello,"));
+  Handle<String> world(isolate->factory()->InternalizeUtf8String(" world!"));
+  Handle<String> cons_str(
+      isolate->factory()->NewConsString(hello, world).ToHandleChecked());
+  test_cases->set(2, *cons_str);
+
+  Handle<String> empty(isolate->factory()->InternalizeUtf8String(""));
+  Handle<String> fake_cons_str(
+      isolate->factory()->NewConsString(expected, empty).ToHandleChecked());
+  test_cases->set(3, *fake_cons_str);
+
+  for (int i = 0; i < 4; ++i) {
+    Handle<String> test = handle(String::cast(test_cases->get(i)));
+    Handle<Object> result = ft.Call(test).ToHandleChecked();
+    CHECK(result->IsString());
+    CHECK(Handle<String>::cast(result)->IsFlat());
+    CHECK(String::Equals(Handle<String>::cast(result), expected));
+  }
+}
+
 TEST(TryToName) {
   typedef CodeStubAssembler::Label Label;
   typedef CodeStubAssembler::Variable Variable;