Fix up gles2 thunk targets a bit

mojo/public/platform/native/BUILD.gn

Index: mojo/public/platform/native/BUILD.gn
diff --git a/mojo/public/platform/native/BUILD.gn b/mojo/public/platform/native/BUILD.gn
index c0cdbae32834ece60b374dc85cdc9d24af0bdcae..a3e720b0a8ac500e68ce29e0c46c50e0af48d54a 100644
--- a/mojo/public/platform/native/BUILD.gn
+++ b/mojo/public/platform/native/BUILD.gn
@@ -24,3 +24,36 @@ source_set("system_thunks") {
   # that all dependent targets remove that link flag. Since GN uses a
   # source_set here, this flag change is not needed.
 }
+
+# GYP version: mojo/mojo_public.gypi:mojo_gles2
+source_set("gles2_thunks") {
+  visibility = [ "//mojo/public/gles2:for_shared_library" ]
+
+  sources = [
+    "gles2_thunks.cc",
+    "gles2_thunks.h",
+    "gles2_impl_thunks.cc",
+    "gles2_impl_thunks.h",
+    "gles2_impl_chromium_texture_mailbox_thunks.cc",
+    "gles2_impl_chromium_texture_mailbox_thunks.h",
+    "gles2_impl_chromium_sync_point_thunks.cc",
+    "gles2_impl_chromium_sync_point_thunks.h",
+  ]
+
+  defines = [
+    "MOJO_GLES2_IMPLEMENTATION",
+  ]
+
+  configs += [ "//third_party/khronos:khronos_headers" ]
+
+  deps = [
+    "//mojo/public/c/gles2",
+    "//mojo/public/c/environment",
+    "//mojo/public/c/system",
+  ]
+
+  if (is_mac) {
+    # TODO(GYP): Make it a run-path dependent library.
+    # 'DYLIB_INSTALL_NAME_BASE': '@loader_path',
+  }
+}