NaCl: create a separate namespace for Mojo handles.

mojo/edk/embedder/BUILD.gn

Index: mojo/edk/embedder/BUILD.gn
diff --git a/mojo/edk/embedder/BUILD.gn b/mojo/edk/embedder/BUILD.gn
index 9650209cf788c25c268bb45c0e39ef6ec21abf8f..29539823bf42171a38ff5992b86e74060eea9b26 100644
--- a/mojo/edk/embedder/BUILD.gn
+++ b/mojo/edk/embedder/BUILD.gn
@@ -16,6 +16,7 @@ mojo_edk_source_set("embedder") {
     "embedder.h",
     "embedder_internal.h",
     "entrypoints.cc",
+    "system_impl_private_entrypoints.cc",
 
     # Test-only code:
     # TODO(vtl): It's a little unfortunate that these end up in the same
@@ -37,6 +38,8 @@ mojo_edk_source_set("embedder") {
     ":platform",
   ]
 
+  mojo_sdk_deps = [ "mojo/public/platform/native:system_impl_private_api" ]
+
   mojo_sdk_public_deps = [ "mojo/public/cpp/system" ]
 
   deps = [