Factor DartLibraryProvider out of DartLoader

sky/engine/tonic/BUILD.gn

Index: sky/engine/tonic/BUILD.gn
diff --git a/sky/engine/tonic/BUILD.gn b/sky/engine/tonic/BUILD.gn
index 3baaf41ddf0c6237d6a10fc1a3318aef99ee0d13..4f37841a6bbd2226783d0f4052f801107eeac263 100644
--- a/sky/engine/tonic/BUILD.gn
+++ b/sky/engine/tonic/BUILD.gn
@@ -13,6 +13,8 @@ source_set("tonic") {
     "dart_class_provider.h",
     "dart_converter.cc",
     "dart_converter.h",
+    "dart_dependency_catcher.cc",
+    "dart_dependency_catcher.h",
     "dart_error.cc",
     "dart_error.h",
     "dart_exception_factory.cc",
@@ -27,8 +29,14 @@ source_set("tonic") {
     "dart_invoke.h",
     "dart_isolate_scope.cc",
     "dart_isolate_scope.h",
+    "dart_library_loader.cc",
+    "dart_library_loader.h",
+    "dart_library_provider.cc",
+    "dart_library_provider.h",
     "dart_persistent_value.cc",
     "dart_persistent_value.h",
+    "dart_snapshot_loader.cc",
+    "dart_snapshot_loader.h",
     "dart_state.cc",
     "dart_state.h",
     "dart_string.cc",
@@ -49,6 +57,7 @@ source_set("tonic") {
 
   deps = [
     "//base",
+    "//mojo/common",
     "//mojo/public/cpp/system",
     "//sky/engine/wtf",
   ]