sdk files reorganization to make dart2js a proper package

pkg/compiler/pubspec.yaml

Index: pkg/compiler/pubspec.yaml
diff --git a/pkg/compiler/pubspec.yaml b/pkg/compiler/pubspec.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..bbccb9a3706f2a39c6dab9a04e4a760eea981475
--- /dev/null
+++ b/pkg/compiler/pubspec.yaml
@@ -0,0 +1,23 @@
+# This pubspec is currently mainly used to make it easier to develop on dart2js
+# by making it a standalone package.
+name: compiler
+#version: do-not-upload
+dependencies:
+  package_config: ^0.0.4
+  js_ast:
+    path: ../js_ast
+  compiler_runtime:
+    path: ../../sdk/lib/_internal/compiler_runtime
+  libraries_spec:
+    path: ../../sdk/lib/_internal/libraries_spec
+
+# Uncomment if running gclient, so you can depend directly on the downloaded
+# versions of dart2js's transitive dependencies:
+#
+# dependency_overrides:
+#   package_config:
+#     path: ../../third_party/pkg/package_config
+#   path:
+#     path: ../../third_party/pkg/path
+#   charcode:
+#     path: ../../third_party/pkg/charcode