Don't use native bridge for non zygote-spawn processes

... unless we force it for testing purposes.

Bug: 26954924
Change-Id: Ib4660a35175abb479d0399e18b6194eb04dbc248
diff --git a/runtime/runtime_options.def b/runtime/runtime_options.def
index 308f3ba..097bccb 100644
--- a/runtime/runtime_options.def
+++ b/runtime/runtime_options.def
@@ -92,6 +92,7 @@
 
 RUNTIME_OPTIONS_KEY (Unit,                DisableExplicitGC)
 RUNTIME_OPTIONS_KEY (Unit,                NoSigChain)
+RUNTIME_OPTIONS_KEY (Unit,                ForceNativeBridge)
 RUNTIME_OPTIONS_KEY (LogVerbosity,        Verbose)
 RUNTIME_OPTIONS_KEY (unsigned int,        LockProfThreshold)
 RUNTIME_OPTIONS_KEY (std::string,         StackTraceFile)