Enable use_once_callback on mojom GN rule by default

third_party/WebKit/public/BUILD.gn

Index: third_party/WebKit/public/BUILD.gn
diff --git a/third_party/WebKit/public/BUILD.gn b/third_party/WebKit/public/BUILD.gn
index a5098adea8079dfcb5543f78f14312a08fcf6e87..2425e40b98c9bf77bfcf4b29eb7c368a2aa47e95 100644
--- a/third_party/WebKit/public/BUILD.gn
+++ b/third_party/WebKit/public/BUILD.gn
@@ -747,6 +747,9 @@ mojom("mojo_bindings") {
   export_class_attribute_blink = "BLINK_PLATFORM_EXPORT"
   export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
   export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
 }
 
 mojom("android_mojo_bindings") {
@@ -771,6 +774,9 @@ mojom("android_mojo_bindings") {
   export_class_attribute_blink = "BLINK_PLATFORM_EXPORT"
   export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
   export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
 }
 
 # The offscreen_canvas_mojo_bindings is separated from the rest of mojom files
@@ -793,7 +799,6 @@ mojom("offscreen_canvas_mojo_bindings") {
   export_class_attribute_blink = "BLINK_PLATFORM_EXPORT"
   export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
   export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
-  use_once_callback = true
 }
 
 group("generate_mojo_bindings") {