Make mojo_system static and mojo_system_impl a component, never use both

mojo/shell/in_process_dynamic_service_runner.cc

Index: mojo/shell/in_process_dynamic_service_runner.cc
diff --git a/mojo/shell/in_process_dynamic_service_runner.cc b/mojo/shell/in_process_dynamic_service_runner.cc
index 9030d59927604cc4c33d5795f78e63f661217603..660418083c31cf94f7737bd074893dea4103d874 100644
--- a/mojo/shell/in_process_dynamic_service_runner.cc
+++ b/mojo/shell/in_process_dynamic_service_runner.cc
@@ -11,6 +11,7 @@
 #include "base/logging.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/scoped_native_library.h"
+#include "mojo/public/platform/native/system_thunks.h"
 
 namespace mojo {
 namespace shell {
@@ -63,6 +64,20 @@ void InProcessDynamicServiceRunner::Run() {
       break;
     }
 
+    MojoSetSystemThunksFn mojo_set_system_thunks_fn =
+        reinterpret_cast<MojoSetSystemThunksFn>(app_library.GetFunctionPointer(
+            "MojoSetSystemThunks"));
+    if (mojo_set_system_thunks_fn) {
+      MojoSystemThunks system_thunks = MojoMakeSystemThunks();
+      size_t expected_size = mojo_set_system_thunks_fn(&system_thunks);
+      if (expected_size > sizeof(MojoSystemThunks)) {
+        LOG(ERROR)
+            << "Invalid DSO. Expected MojoSystemThunks size: "
+            << expected_size;
+        break;
+      }
+    }
+
     typedef MojoResult (*MojoMainFunction)(MojoHandle);
     MojoMainFunction main_function = reinterpret_cast<MojoMainFunction>(
         app_library.GetFunctionPointer("MojoMain"));