Merge the tonic layer from skydart branch back to master

sky/engine/tonic/dart_string.cc

Index: sky/engine/tonic/dart_string.cc
diff --git a/sky/engine/tonic/dart_string.cc b/sky/engine/tonic/dart_string.cc
new file mode 100644
index 0000000000000000000000000000000000000000..98550314cb906ad3a04ea1b03b927870481c15bb
--- /dev/null
+++ b/sky/engine/tonic/dart_string.cc
@@ -0,0 +1,65 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sky/engine/config.h"
+#include "sky/engine/tonic/dart_string.h"
+
+#include "base/logging.h"
+
+namespace blink {
+namespace {
+
+void FinalizeString(void* string_impl) {
+  DCHECK(string_impl);
+  reinterpret_cast<StringImpl*>(string_impl)->deref();
+}
+
+template <typename CharType>
+String Externalize(Dart_Handle handle, intptr_t length) {
+  if (!length)
+    return StringImpl::empty();
+  CharType* buffer = nullptr;
+  RefPtr<StringImpl> string_impl =
+      StringImpl::createUninitialized(length, buffer);
+
+  string_impl->ref();  // Balanced in FinalizeString.
+
+  Dart_Handle result =
+      Dart_MakeExternalString(handle, buffer, length * sizeof(CharType),
+                              string_impl.get(), FinalizeString);
+  DCHECK(!Dart_IsError(result));
+  return String(string_impl.release());
+}
+
+}  // namespace
+
+Dart_Handle CreateDartString(StringImpl* string_impl) {
+  if (!string_impl)
+    return Dart_EmptyString();
+
+  string_impl->ref();  // Balanced in FinalizeString.
+
+  if (string_impl->is8Bit()) {
+    return Dart_NewExternalLatin1String(string_impl->characters8(),
+                                        string_impl->length(), string_impl,
+                                        FinalizeString);
+  } else {
+    return Dart_NewExternalUTF16String(string_impl->characters16(),
+                                       string_impl->length(), string_impl,
+                                       FinalizeString);
+  }
+}
+
+String ExternalizeDartString(Dart_Handle handle) {
+  DCHECK(Dart_IsString(handle));
+  DCHECK(!Dart_IsExternalString(handle));
+  bool is_latin1 = Dart_IsStringLatin1(handle);
+  intptr_t length;
+  Dart_StringLength(handle, &length);
+  if (is_latin1)
+    return Externalize<LChar>(handle, length);
+  return Externalize<UChar>(handle, length);
+}
+
+}  // namespace blink