Fix signed/unsigned comparison mismatch

mojo/android/system/core_impl.cc

Index: mojo/android/system/core_impl.cc
diff --git a/mojo/android/system/core_impl.cc b/mojo/android/system/core_impl.cc
index 1971cac10e5f76fcebdb9b7082221ab0aa596c65..55a374e50bcba68e1bff0ef41548c9278b2052a6 100644
--- a/mojo/android/system/core_impl.cc
+++ b/mojo/android/system/core_impl.cc
@@ -163,7 +163,7 @@ static jint Wait(JNIEnv* env,
   DCHECK(buffer_start);
   DCHECK_EQ(reinterpret_cast<const uintptr_t>(buffer_start) % 8, 0u);
   DCHECK_EQ(sizeof(struct MojoHandleSignalsState),
-            env->GetDirectBufferCapacity(buffer));
+            static_cast<size_t>(env->GetDirectBufferCapacity(buffer)));
   struct MojoHandleSignalsState* signals_state =
       static_cast<struct MojoHandleSignalsState*>(buffer_start);
   return MojoWait(mojo_handle, signals, deadline, signals_state);