Update clang, re-enable checker, fix issues it flags

services/files/file_impl.h

Index: services/files/file_impl.h
diff --git a/services/files/file_impl.h b/services/files/file_impl.h
index 58fa94cca4648964f1ab98ce15496a621f14b285..355b11799f5d5b5314b47aab4915277f05dfcfad 100644
--- a/services/files/file_impl.h
+++ b/services/files/file_impl.h
@@ -55,7 +55,7 @@ class FileImpl : public File {
   void AsBuffer(const AsBufferCallback& callback) override;
   void Ioctl(uint32_t request,
              Array<uint32_t> in_values,
-             const IoctlCallback& callback);
+             const IoctlCallback& callback) override;
 
  private:
   StrongBinding<File> binding_;