Added libmedia_datasource_headers header library

This exports the 'include' directory of libmedia only. It does
not export any additional header libraries. This can be used
by modules which require only header files from libmedia.

Test: Build libmedia_datasource_headers
Bug: 151789258

Change-Id: I1814f07e29ea0b8a7db6e7f8657ffcba6ef582e7
diff --git a/media/libmedia/Android.bp b/media/libmedia/Android.bp
index b56ea56..6a8f981 100644
--- a/media/libmedia/Android.bp
+++ b/media/libmedia/Android.bp
@@ -15,6 +15,18 @@
     ],
 }
 
+cc_library_headers {
+    name: "libmedia_datasource_headers",
+    export_include_dirs: ["include"],
+    host_supported: true,
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
+    apex_available: ["com.android.media"],
+}
+
 filegroup {
     name: "libmedia_omx_aidl",
     srcs: [