Optionally use new GN optimization config.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index d6341f7449d6674354e462261e0ab250101694c9..23108b9b5e737111832a2e6da2dcc4f5528f740e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1534,7 +1534,11 @@ source_set("v8_base") {
   ]
 
   if (!is_debug) {
-    configs -= [ "//build/config/compiler:optimize" ]
+    if (using_new_optimization_config) {
+      configs -= [ "//build/config/compiler:default_optimization" ]
+    } else {
+      configs -= [ "//build/config/compiler:optimize" ]
+    }
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 
@@ -1633,7 +1637,11 @@ source_set("v8_libbase") {
   ]
 
   if (!is_debug) {
-    configs -= [ "//build/config/compiler:optimize" ]
+    if (using_new_optimization_config) {
+      configs -= [ "//build/config/compiler:default_optimization" ]
+    } else {
+      configs -= [ "//build/config/compiler:optimize" ]
+    }
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 
@@ -1700,7 +1708,11 @@ source_set("v8_libplatform") {
   ]
 
   if (!is_debug) {
-    configs -= [ "//build/config/compiler:optimize" ]
+    if (using_new_optimization_config) {
+      configs -= [ "//build/config/compiler:default_optimization" ]
+    } else {
+      configs -= [ "//build/config/compiler:optimize" ]
+    }
     configs += [ "//build/config/compiler:optimize_max" ]
   }