Separate cc_library_headers to its own file and add tests

Preparation for adding cc_library_headers to sdk.

Bug: 148933848
Test: m nothing
Change-Id: Icbc86b21f44dc79393b82be339cf3b133cbf9d8c

cc/library_headers.go

@@ -0,0 +1,35 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cc
+
+import "android/soong/android"
+
+func init() {
+	RegisterLibraryHeadersBuildComponents(android.InitRegistrationContext)
+}
+
+func RegisterLibraryHeadersBuildComponents(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("cc_library_headers", LibraryHeaderFactory)
+}
+
+// cc_library_headers contains a set of c/c++ headers which are imported by
+// other soong cc modules using the header_libs property. For best practices,
+// use export_include_dirs property or LOCAL_EXPORT_C_INCLUDE_DIRS for
+// Make.
+func LibraryHeaderFactory() android.Module {
+	module, library := NewLibrary(android.HostAndDeviceSupported)
+	library.HeaderOnly()
+	return module.Init()
+}