Add nplb sources to fix include check on android (#4638)

These sources were removed from nplb for android platforms during the
migration of nplb from older branches. I couldn't find a reason for
their removal, and adding them back resolves a gn include check.

b/377295011

starboard/nplb/BUILD.gn

@@ -47,6 +47,8 @@ test("nplb") {
     "//starboard/nplb/sabi/struct_alignment_test.cc",
     "//starboard/shared/starboard/drm/drm_test_helpers.cc",
     "//starboard/shared/starboard/drm/drm_test_helpers.h",
+    "//starboard/testing/fake_graphics_context_provider.cc",
+    "//starboard/testing/fake_graphics_context_provider.h",
     "align_test.cc",
     "audio_sink_create_test.cc",
     "audio_sink_destroy_test.cc",
@@ -219,8 +221,6 @@ test("nplb") {
 
   if (!is_android) {
     sources += [
-      "//starboard/testing/fake_graphics_context_provider.cc",
-      "//starboard/testing/fake_graphics_context_provider.h",
       "maximum_player_configuration_explorer_test.cc",
       "media_set_audio_write_duration_test.cc",
       "multiple_player_test.cc",

starboard/nplb/maximum_player_configuration_explorer.h

@@ -23,8 +23,7 @@
 #include "starboard/nplb/player_test_util.h"
 #include "starboard/player.h"
 #include "starboard/shared/starboard/media/media_util.h"
-// TODO(cobalt, b/377295011): remove the nogncheck annotation.
-#include "starboard/testing/fake_graphics_context_provider.h"  // nogncheck
+#include "starboard/testing/fake_graphics_context_provider.h"
 
 namespace starboard {
 namespace nplb {