Use base::MakeFixedFlatSet for never-sniffed mime types.

It's slightly more efficient.

Change-Id: I1bbc9e2ad89b82c81b67a3b3df615879a8d7519e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2562821
Auto-Submit: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832645}

services/network/public/cpp/cross_origin_read_blocking.cc

@@ -14,7 +14,7 @@
 
 #include "base/check_op.h"
 #include "base/command_line.h"
-#include "base/containers/flat_set.h"
+#include "base/containers/fixed_flat_set.h"
 #include "base/feature_list.h"
 #include "base/lazy_instance.h"
 #include "base/metrics/histogram_macros.h"
@@ -248,12 +248,14 @@ void BlockResponseHeaders(
 // disclosure of "application/zip" even though Chrome doesn't have built-in
 // support for this resource type.  And CORB also wants to protect
 // "application/pdf" even though Chrome happens to support this resource type.
-base::flat_set<std::string>& GetNeverSniffedMimeTypes() {
-  static base::NoDestructor<base::flat_set<std::string>> s_types{{
+const auto& GetNeverSniffedMimeTypes() {
+  static constexpr auto kNeverSniffedMimeTypes = base::MakeFixedFlatSet<
+      base::StringPiece>({
+      // clang-format off
       // The types below (zip, protobuf, etc.) are based on most commonly used
       // content types according to HTTP Archive - see:
       // https://github.com/whatwg/fetch/issues/860#issuecomment-457330454
-            "application/gzip",
+      "application/gzip",
       "application/x-gzip",
       "application/x-protobuf",
       "application/zip",
@@ -308,15 +310,16 @@ base::flat_set<std::string>& GetNeverSniffedMimeTypes() {
       "multipart/byteranges",
       // TODO(lukasza): https://crbug.com/802836#c11: Add
       // application/signed-exchange.
-  }};
+      // clang-format on
+  });
 
   // All items need to be lower-case, to support case-insensitive comparisons
   // later.
-  DCHECK(std::all_of(
-      s_types->begin(), s_types->end(),
-      [](const std::string& s) { return s == base::ToLowerASCII(s); }));
+  DCHECK(std::all_of(kNeverSniffedMimeTypes.begin(),
+                     kNeverSniffedMimeTypes.end(),
+                     [](const auto& s) { return s == base::ToLowerASCII(s); }));
 
-  return *s_types;
+  return kNeverSniffedMimeTypes;
 }
 
 }  // namespace