Add html_common to .gni files.

This will enable a fix to an unresolved export that causes Dartdoc
to complain about all Flutter packages.

Bug: dart-lang/dartdoc#2143
Change-Id: I634e21066420b100295989cf9bdcd35af91a617b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143020
Reviewed-by: Devon Carew <[email protected]>
Commit-Queue: Janice Collins <[email protected]>

Author: jcollins-g

sdk/lib/html/html_common/html_common_sources.gni

@@ -0,0 +1,14 @@
+# Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+html_common_sdk_sources = [
+  "conversions.dart",
+  "conversions_dart2js.dart",
+  "css_class_set.dart",
+  "device.dart",
+  "filtered_element_list.dart",
+  "html_common_dart2js.dart",
+  "lists.dart",
+  "metadata.dart",
+]

sdk_nnbd/lib/html/html_common/html_common_sources.gni

@@ -0,0 +1,14 @@
+# Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+html_common_sdk_sources = [
+  "conversions.dart",
+  "conversions_dart2js.dart",
+  "css_class_set.dart",
+  "device.dart",
+  "filtered_element_list.dart",
+  "html_common_dart2js.dart",
+  "lists.dart",
+  "metadata.dart",
+]