Expose the GC under a name that is less collision prone than window.gc.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 9c9362b2f003d5e648b8186813d8fe85da300b70..b46901162c7694508b87dffd34d3700b682921b8 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -344,6 +344,10 @@ DEFINE_bool(enable_vldr_imm, false,
 DEFINE_string(expose_natives_as, NULL, "expose natives in global object")
 DEFINE_string(expose_debug_as, NULL, "expose debug in global object")
 DEFINE_bool(expose_gc, false, "expose gc extension")
+DEFINE_string(expose_gc_as,
+              NULL,
+              "expose gc extension under the specified name")
+DEFINE_implication(expose_gc_as, expose_gc)
 DEFINE_bool(expose_externalize_string, false,
             "expose externalize string extension")
 DEFINE_int(stack_trace_limit, 10, "number of stack frames to capture")