Fix remaining warnings for -Wmissing-braces and enable on win clang.

third_party/iaccessible2/BUILD.gn

Index: third_party/iaccessible2/BUILD.gn
diff --git a/third_party/iaccessible2/BUILD.gn b/third_party/iaccessible2/BUILD.gn
index 6ebcee644d3d0c166e4fefc5a5a73e1de95f5892..902667464257dfef2b771b02e4112a2cd6fe80e9 100644
--- a/third_party/iaccessible2/BUILD.gn
+++ b/third_party/iaccessible2/BUILD.gn
@@ -20,8 +20,15 @@ shared_library("IAccessible2Proxy") {
     "IAccessible2Proxy.def",
   ]
 
+  config("IAccessible2Proxy_warnings") {
+    if (is_clang) {
+      # MIDL generated code has a habit of omitting optional braces.
+      cflags = [ "-Wno-missing-braces" ]
+    }
+  }
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
+  configs += [ ":IAccessible2Proxy_warnings" ]
 
   defines = [ "REGISTER_PROXY_DLL" ]