Merge the tonic layer from skydart branch back to master

sky/engine/tonic/BUILD.gn

+# 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.
+
+source_set("tonic") {
+  sources = [
+    "dart_api_scope.h",
+    "dart_builtin.cc",
+    "dart_builtin.h",
+    "dart_class_library.cc",
+    "dart_class_library.h",
+    "dart_class_provider.cc",
+    "dart_class_provider.h",
+    "dart_converter.cc",
+    "dart_converter.h",
+    "dart_error.cc",
+    "dart_error.h",
+    "dart_gc_context.cc",
+    "dart_gc_context.h",
+    "dart_gc_controller.cc",
+    "dart_gc_controller.h",
+    "dart_gc_visitor.cc",
+    "dart_gc_visitor.h",
+    "dart_isolate_scope.cc",
+    "dart_isolate_scope.h",
+    "dart_persistent_value.cc",
+    "dart_persistent_value.h",
+    "dart_state.cc",
+    "dart_state.h",
+    "dart_string.cc",
+    "dart_string.h",
+    "dart_string_cache.cc",
+    "dart_string_cache.h",
+    "dart_value.cc",
+    "dart_value.h",
+    "dart_wrappable.cc",
+    "dart_wrappable.h",
+    "dart_wrapper_info.h",
+  ]
+
+  deps = [
+    "//base",
+    "//sky/engine/wtf",
+  ]
+
+  public_deps = [
+    "//dart/runtime/bin:libdart_withcore",
+  ]
+}