bindings: Move definition of a GN flag

Move definition of use_blink_v8_binding_new_idl_dictionary to
t/b/r/config.gni and define a C++ definition.

Bug: 839389
Change-Id: I8ebe279ad03af81ceb81a5856119eb3097a379b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2358930
Auto-Submit: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798492}

third_party/blink/renderer/bindings/bindings.gni

@@ -7,12 +7,6 @@
 
 import("//third_party/blink/renderer/bindings/modules/v8/v8.gni")
 
-declare_args() {
-  # If this variable is set true, we use a new code generator to generate code
-  # of IDL dictionaries.  See https://crbug.com/839389 for the details.
-  use_blink_v8_binding_new_idl_dictionary = false
-}
-
 bindings_core_v8_files =
     get_path_info([
                     "core/v8/active_script_wrappable.cc",

third_party/blink/renderer/config.gni

@@ -40,6 +40,10 @@ declare_args() {
   # If true, webgl2-compute context will be supported.
   support_webgl2_compute_context = !is_android
 
+  # If true, the new implementation (experimental) of Blink-V8 bindings
+  # (of IDL dictionary) is used.
+  use_blink_v8_binding_new_idl_dictionary = false
+
   # If true, the new implementation (experimental) of Blink-V8 bindings
   # (of IDL interface) is used.
   use_blink_v8_binding_new_idl_interface = true
@@ -65,6 +69,10 @@ if (use_webaudio_pffft) {
   feature_defines_list += [ "WTF_USE_WEBAUDIO_PFFFT=1" ]
 }
 
+if (use_blink_v8_binding_new_idl_dictionary) {
+  feature_defines_list += [ "USE_BLINK_V8_BINDING_NEW_IDL_DICTIONARY" ]
+}
+
 if (use_blink_v8_binding_new_idl_interface) {
   feature_defines_list += [ "USE_BLINK_V8_BINDING_NEW_IDL_INTERFACE" ]
 }