Make the offset of SetIndexBuffer default to 0

BUG=dawn:22

Change-Id: Icc4f03c3f49b610ef5f620b4c26a6ae24ed6c774
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/12040
Reviewed-by: François Beaufort <beaufort.francois@gmail.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/dawn.json b/dawn.json
index 588436a..81d9914 100644
--- a/dawn.json
+++ b/dawn.json
@@ -891,7 +891,7 @@
                 "name": "set index buffer",
                 "args": [
                     {"name": "buffer", "type": "buffer"},
-                    {"name": "offset", "type": "uint64_t"}
+                    {"name": "offset", "type": "uint64_t", "default": "0"}
                 ]
             },
             {
@@ -1076,7 +1076,7 @@
                 "name": "set index buffer",
                 "args": [
                     {"name": "buffer", "type": "buffer"},
-                    {"name": "offset", "type": "uint64_t"}
+                    {"name": "offset", "type": "uint64_t", "default": "0"}
                 ]
             },
             {