Split apart the PPAPI GN targets

ppapi/c/BUILD.gn

Index: ppapi/c/BUILD.gn
diff --git a/testing/legion/__init__.py b/ppapi/c/BUILD.gn
similarity index 51%
copy from testing/legion/__init__.py
copy to ppapi/c/BUILD.gn
index 50b23dff631dbfd12f490f20fe2a2871179b73b9..5b6def592cf5f2845f315cb43bc970163d22fcfd 100644
--- a/testing/legion/__init__.py
+++ b/ppapi/c/BUILD.gn
@@ -1,3 +1,10 @@
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
+# found in the LICENSE file.
+
+import("//ppapi/ppapi_sources.gni")
+
+# These are just headers.
+source_set("c") {
+  sources = rebase_path(ppapi_sources.c_source_files, ".", "..")
+}