[NativeFS] Allow single accepted extension without wrapping in array.

This implements the change from https://github.com/WICG/native-file-system/pull/207

Change-Id: Ib496775f1c7e1a2c7b4be4f56232739acfc0d020
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2311054Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Auto-Submit: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791255}

content/browser/native_file_system/file_system_chooser_browsertest.cc

@@ -487,14 +487,15 @@ IN_PROC_BROWSER_TEST_F(FileSystemChooserBrowserTest, AcceptsOptions) {
       EvalJs(shell(),
              "self.showOpenFilePicker({types: ["
              "  {description: 'foo', accept: {'text/custom': ['txt', 'Js']}},"
-             "  {accept: {'image/jpeg': []}}"
+             "  {accept: {'image/jpeg': []}},"
+             "  {accept: {'image/svg+xml': 'svg'}},"
              "]})");
   EXPECT_TRUE(result.error.find("aborted") != std::string::npos)
       << result.error;
 
   ASSERT_TRUE(dialog_params.file_types);
   EXPECT_TRUE(dialog_params.file_types->include_all_files);
-  ASSERT_EQ(2u, dialog_params.file_types->extensions.size());
+  ASSERT_EQ(3u, dialog_params.file_types->extensions.size());
   ASSERT_EQ(2u, dialog_params.file_types->extensions[0].size());
   EXPECT_EQ(FILE_PATH_LITERAL("txt"),
             dialog_params.file_types->extensions[0][0]);
@@ -504,8 +505,10 @@ IN_PROC_BROWSER_TEST_F(FileSystemChooserBrowserTest, AcceptsOptions) {
                              FILE_PATH_LITERAL("jpg")));
   EXPECT_TRUE(base::Contains(dialog_params.file_types->extensions[1],
                              FILE_PATH_LITERAL("jpeg")));
+  EXPECT_TRUE(base::Contains(dialog_params.file_types->extensions[2],
+                             FILE_PATH_LITERAL("svg")));
 
-  ASSERT_EQ(2u,
+  ASSERT_EQ(3u,
             dialog_params.file_types->extension_description_overrides.size());
   EXPECT_EQ(base::ASCIIToUTF16("foo"),
             dialog_params.file_types->extension_description_overrides[0]);

third_party/blink/renderer/bindings/modules/v8/generated.gni

@@ -111,6 +111,8 @@ bindings_modules_generated_union_type_files = [
   "$bindings_modules_v8_output_dir/unsigned_long_enforce_range_sequence_or_gpu_origin_3d_dict.h",
   "$bindings_modules_v8_output_dir/usv_string_or_uint32_array.cc",
   "$bindings_modules_v8_output_dir/usv_string_or_uint32_array.h",
+  "$bindings_modules_v8_output_dir/usv_string_or_usv_string_sequence.cc",
+  "$bindings_modules_v8_output_dir/usv_string_or_usv_string_sequence.h",
   "$bindings_modules_v8_output_dir/webgl_rendering_context_or_webgl2_rendering_context.cc",
   "$bindings_modules_v8_output_dir/webgl_rendering_context_or_webgl2_rendering_context.h",
   "$bindings_modules_v8_output_dir/worklet_animation_effect_or_worklet_group_effect.cc",

third_party/blink/renderer/modules/native_file_system/file_picker_accept_type.idl

@@ -5,5 +5,5 @@
 // https://wicg.github.io/native-file-system/#dictdef-filepickeraccepttype
 dictionary FilePickerAcceptType {
   USVString description;
-  record<USVString, sequence<USVString>> accept;
+  record<USVString, (USVString or sequence<USVString>)> accept;
 };

third_party/blink/renderer/modules/native_file_system/global_native_file_system.cc

@@ -102,7 +102,10 @@ Vector<mojom::blink::ChooseFileSystemEntryAcceptsOptionPtr> ConvertAccepts(
       }
 
       mimeTypes.push_back(type);
-      extensions.AppendVector(a.second);
+      if (a.second.IsUSVString())
+        extensions.push_back(a.second.GetAsUSVString());
+      else
+        extensions.AppendVector(a.second.GetAsUSVStringSequence());
     }
     result.emplace_back(
         blink::mojom::blink::ChooseFileSystemEntryAcceptsOption::New(