Make wgpu::BindGroupLayoutEntry extensible

Bug: dawn:22
Change-Id: Ifce24a0b19fb8d3acb6ac8ab32f3f3e22a248b3b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/39340
Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Stephen White <senorblanco@chromium.org>
diff --git a/dawn.json b/dawn.json
index 2834a86..ec91cd2 100644
--- a/dawn.json
+++ b/dawn.json
@@ -163,7 +163,7 @@
 
     "bind group layout entry": {
         "category": "structure",
-        "extensible": false,
+        "extensible": true,
         "members": [
             {"name": "binding", "type": "uint32_t"},
             {"name": "visibility", "type": "shader stage"},
diff --git a/src/tests/unittests/wire/WireArgumentTests.cpp b/src/tests/unittests/wire/WireArgumentTests.cpp
index f39fa20..401f9b8 100644
--- a/src/tests/unittests/wire/WireArgumentTests.cpp
+++ b/src/tests/unittests/wire/WireArgumentTests.cpp
@@ -307,7 +307,8 @@
 TEST_F(WireArgumentTests, StructureOfStructureArrayArgument) {
     static constexpr int NUM_BINDINGS = 3;
     WGPUBindGroupLayoutEntry entries[NUM_BINDINGS]{
-        {0,
+        {nullptr,
+         0,
          WGPUShaderStage_Vertex,
          WGPUBindingType_Sampler,
          false,
@@ -319,7 +320,8 @@
          {},
          {},
          {}},
-        {1,
+        {nullptr,
+         1,
          WGPUShaderStage_Vertex,
          WGPUBindingType_SampledTexture,
          false,
@@ -331,7 +333,8 @@
          {},
          {},
          {}},
-        {2,
+        {nullptr,
+         2,
          static_cast<WGPUShaderStage>(WGPUShaderStage_Vertex | WGPUShaderStage_Fragment),
          WGPUBindingType_UniformBuffer,
          false,