Add Observatory to sky dart_controller

sky/shell/BUILD.gn

Index: sky/shell/BUILD.gn
diff --git a/sky/shell/BUILD.gn b/sky/shell/BUILD.gn
index c25f5dbdd70d95d3467c8d4e82d3e7be9204aa69..bdd68d5461bc34f3da0d99166391e2e1c47765b8 100644
--- a/sky/shell/BUILD.gn
+++ b/sky/shell/BUILD.gn
@@ -50,6 +50,19 @@ shared_library("sky_shell") {
     "ui_delegate.h",
   ]
 
+  include_dirs = [
+    # Needed for 'dart:io' event handler (used in sky_main.cc).
+    rebase_path("//dart/runtime"),
+  ]
+
+  # Needed to satisfy //dart/runtime/bin/assert.h
+  defines = []
+  if (!is_debug) {
+    defines += [ "NDEBUG" ]
+  } else {
+    defines += [ "DEBUG" ]
+  }
+
   deps = [
     "//base",
     "//base:i18n",