Small clean up of externalizing strings.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/462643002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23043 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/api.cc

@@ -5475,7 +5475,7 @@ Local<String> v8::String::NewExternal(
 bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
   i::Handle<i::String> obj = Utils::OpenHandle(this);
   i::Isolate* isolate = obj->GetIsolate();
-  if (i::StringShape(*obj).IsExternalTwoByte()) {
+  if (i::StringShape(*obj).IsExternal()) {
     return false;  // Already an external string.
   }
   ENTER_V8(isolate);
@@ -5488,6 +5488,8 @@ bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
   CHECK(resource && resource->data());
 
   bool result = obj->MakeExternal(resource);
+  // Assert that if CanMakeExternal(), then externalizing actually succeeds.
+  DCHECK(!CanMakeExternal() || result);
   if (result) {
     DCHECK(obj->IsExternalString());
     isolate->heap()->external_string_table()->AddString(*obj);
@@ -5515,7 +5517,7 @@ bool v8::String::MakeExternal(
     v8::String::ExternalAsciiStringResource* resource) {
   i::Handle<i::String> obj = Utils::OpenHandle(this);
   i::Isolate* isolate = obj->GetIsolate();
-  if (i::StringShape(*obj).IsExternalTwoByte()) {
+  if (i::StringShape(*obj).IsExternal()) {
     return false;  // Already an external string.
   }
   ENTER_V8(isolate);
@@ -5528,6 +5530,8 @@ bool v8::String::MakeExternal(
   CHECK(resource && resource->data());
 
   bool result = obj->MakeExternal(resource);
+  // Assert that if CanMakeExternal(), then externalizing actually succeeds.
+  DCHECK(!CanMakeExternal() || result);
   if (result) {
     DCHECK(obj->IsExternalString());
     isolate->heap()->external_string_table()->AddString(*obj);

src/factory.cc

@@ -270,6 +270,7 @@ MaybeHandle<String> Factory::NewStringFromTwoByte(Vector<const uc16> string,
   int length = string.length();
   const uc16* start = string.start();
   if (String::IsOneByte(start, length)) {
+    if (length == 1) return LookupSingleCharacterStringFromCode(string[0]);
     Handle<SeqOneByteString> result;
     ASSIGN_RETURN_ON_EXCEPTION(
         isolate(),

src/objects.cc

@@ -1052,11 +1052,10 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
                   resource->length() * sizeof(smart_chars[0])) == 0);
   }
 #endif  // DEBUG
-  Heap* heap = GetHeap();
   int size = this->Size();  // Byte size of the original string.
-  if (size < ExternalString::kShortSize) {
-    return false;
-  }
+  // Abort if size does not allow in-place conversion.
+  if (size < ExternalString::kShortSize) return false;
+  Heap* heap = GetHeap();
   bool is_ascii = this->IsOneByteRepresentation();
   bool is_internalized = this->IsInternalizedString();
 
@@ -1109,6 +1108,9 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
 
 
 bool String::MakeExternal(v8::String::ExternalAsciiStringResource* resource) {
+  // Externalizing twice leaks the external resource, so it's
+  // prohibited by the API.
+  DCHECK(!this->IsExternalString());
 #ifdef ENABLE_SLOW_DCHECKS
   if (FLAG_enable_slow_asserts) {
     // Assert that the resource and the string are equivalent.
@@ -1125,11 +1127,10 @@ bool String::MakeExternal(v8::String::ExternalAsciiStringResource* resource) {
                   resource->length() * sizeof(smart_chars[0])) == 0);
   }
 #endif  // DEBUG
-  Heap* heap = GetHeap();
   int size = this->Size();  // Byte size of the original string.
-  if (size < ExternalString::kShortSize) {
-    return false;
-  }
+  // Abort if size does not allow in-place conversion.
+  if (size < ExternalString::kShortSize) return false;
+  Heap* heap = GetHeap();
   bool is_internalized = this->IsInternalizedString();
 
   // Morph the string to an external string by replacing the map and