Revert "[sdk] Remove dart SDK."

This reverts commit 8c78205007e1626c73780a124ff418e778ab04a2.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [sdk] Remove dart SDK.
> 
> Test: built fine.
> Bug: DX-730 #done
> Change-Id: I551848aab6bd4bb325643a79c3ce646362b5effd

TBR=pylaligand@google.com,jinwoo@google.com

Change-Id: I754705ecdf93516e25ad00d13a2085cedbba675c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: DX-730 #done
diff --git a/packages/sdk/all b/packages/sdk/all
index 0a5ae1b..ee9c174 100644
--- a/packages/sdk/all
+++ b/packages/sdk/all
@@ -1,5 +1,6 @@
 {
   "imports": [
+    "topaz/packages/sdk/dart",
     "topaz/packages/sdk/topaz"
   ]
 }
diff --git a/packages/sdk/dart b/packages/sdk/dart
new file mode 100644
index 0000000..c881f02
--- /dev/null
+++ b/packages/sdk/dart
@@ -0,0 +1,5 @@
+{
+  "labels": [
+    "//topaz/public/sdk:dart"
+  ]
+}
diff --git a/public/sdk/BUILD.gn b/public/sdk/BUILD.gn
index 082bd49..9c966f1 100644
--- a/public/sdk/BUILD.gn
+++ b/public/sdk/BUILD.gn
@@ -6,6 +6,19 @@
 import("//build/sdk/sdk.gni")
 import("//build/sdk/sdk_molecule.gni")
 
+sdk("dart") {
+  category = "partner"
+
+  deps = [
+    "//topaz/public/dart/fidl:fidl_sdk($dart_toolchain)",
+    "//topaz/public/dart/widgets:lib.widgets_sdk($dart_toolchain)",
+    "//topaz/public/lib/app_driver/dart:dart_sdk($dart_toolchain)",
+    "//topaz/public/lib/app/dart:dart_sdk($dart_toolchain)",
+    "//topaz/public/lib/config/dart:config_sdk($dart_toolchain)",
+    "//topaz/public/lib/schemas/dart:dart_sdk($dart_toolchain)",
+  ]
+}
+
 # Tools and libraries required to generate and use FIDL bindings in Dart.
 sdk_molecule("fidl_dart") {
   deps = [