CodeGen: Make DefaultValueExpr have dependencies

We used to use an empty ScriptValue as a default null value,
and we will distinguish them in the new code generator.
Then we found the default value expressions need to know what
they depend on, such as a null value for ScriptValue type
needs v8::Isolate.

This CL makes DefaultValueExpr dataset to have dependency information
to work for the case.


Bug: 839389, 1070964
Change-Id: I19dd7a109bb1752df6c53a502ea2fd815fd3c348
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2198764Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770962}

third_party/blink/renderer/bindings/scripts/bind_gen/dictionary.py

@@ -315,9 +315,9 @@ def make_dict_member_vars(cg_context):
     if member.default_value:
         default_expr = make_default_value_expr(member.idl_type,
                                                member.default_value)
-        if default_expr.initializer is not None:
+        if default_expr.initializer_expr is not None:
             default_value_initializer = _format("{{{}}}",
-                                                default_expr.initializer)
+                                                default_expr.initializer_expr)
 
     _1 = blink_type_info(member.idl_type).member_t
     _2 = _blink_member_name(member).value_var