[gn] Experiment: Reset -O3 to -O2.

gni/v8.gni

Index: gni/v8.gni
diff --git a/gni/v8.gni b/gni/v8.gni
index 93b766920a7c71bfc7e10d1b36fea5902390a8f5..011e1451d3a26b26840b5b959aefcaa38f1d587e 100644
--- a/gni/v8.gni
+++ b/gni/v8.gni
@@ -57,7 +57,7 @@ if (is_debug && !v8_optimized_debug) {
   # TODO(crbug.com/621335) Rework this so that we don't have the confusion
   # between "optimize_speed" and "optimize_max".
   if (is_posix && !is_android && !is_nacl && !using_sanitizer) {
-    add_configs += [ "//build/config/compiler:optimize_speed" ]
+    add_configs += [ "//build/config/compiler:optimize_max" ]
   } else {
     add_configs += [ "//build/config/compiler:optimize_max" ]
   }