Allow assertions to be enabled in Blink Release builds.

Source/config.gni

Index: Source/config.gni
diff --git a/Source/config.gni b/Source/config.gni
index a317eb896785d803db937e5be7e47d9f12308e38..c566161baa2425822e703969461234510c74d384 100644
--- a/Source/config.gni
+++ b/Source/config.gni
@@ -25,6 +25,8 @@ declare_args() {
   # garbage-collection infrastructure during compilation.
   blink_gc_plugin = false
   blink_gc_plugin_dump_graph = false
+
+  blink_asserts_always_on = false
 }
 
 use_default_render_theme = use_aura
@@ -94,6 +96,9 @@ if (use_default_render_theme) {
 if (enable_oilpan) {
   feature_defines_list += [ "ENABLE_OILPAN=1" ]
 }
+if (blink_asserts_always_on) {
+  feature_defines_list += [ "ENABLE_ASSERT=1" ]
+}
 
 # feature_defines_string -------------------------------------------------------