Enable C++17 on linux (including in CFI builds)

The prerequisite rolled in in
https://chromium-review.googlesource.com/c/chromium/src/+/3315436

With this, all platforms use -std=c++17.
Please don't rely on that yet though:
- it's not yet clear that this is going to stick
- we'll send out guidelines on how we'll adopt C++17 features

Bug: 1273966,752720
Cq-Include-Trybots: luci.chromium.try:linux_chromium_cfi_rel_ng
Change-Id: Icda9a95b159b8ae6fd1f74095fea7913343d210a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3308459
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#948345}

base/strings/string_util.cc

@@ -21,7 +21,6 @@
 #include <type_traits>
 #include <vector>
 
-#include "base/cfi_buildflags.h"
 #include "base/check_op.h"
 #include "base/cxx17_backports.h"
 #include "base/no_destructor.h"
@@ -35,12 +34,9 @@ namespace base {
 
 bool IsWprintfFormatPortable(const wchar_t* format) {
   // This snippet of code checks that we can build C++17 code.
-  // TODO(thakis): Enable this on all platforms, and then remove it again.
-#if !defined(OS_LINUX) && !BUILDFLAG(CFI_ICALL_CHECK) && \
-    !BUILDFLAG(CFI_CAST_CHECK)
+  // TODO(thakis): Remove this again in a bit.
   if constexpr (constexpr int i = 0; i > 0) {
   }
-#endif
 
   for (const wchar_t* position = format; *position != '\0'; ++position) {
     if (*position == '%') {

base/template_util.h

@@ -247,13 +247,7 @@ struct negation : bool_constant<!static_cast<bool>(B::value)> {};
 // [1] https://en.cppreference.com/w/cpp/types/result_of
 // [2] https://wg21.link/meta.trans.other#lib:invoke_result
 template <typename Functor, typename... Args>
-#if __cplusplus >= 201703
-// result_of is deprecated in c++17, so don't use it there.
 using invoke_result = std::invoke_result<Functor, Args...>;
-#else
-// TODO(thakis): Remove this branch once all platforms use C++17.
-using invoke_result = std::result_of<Functor && (Args && ...)>;
-#endif
 
 // Implementation of C++17's std::invoke_result_t.
 //

build/config/compiler/BUILD.gn

@@ -586,10 +586,7 @@ config("compiler") {
     }
 
     cflags_c += [ "-std=${standard_prefix}11" ]
-
-    # TODO(https://crbug.com/1273966): Use C++17 with is_cfi and is_linux once
-    # CFI works with -std=c++17.
-    if ((is_nacl && !is_nacl_saigo) || is_cfi || is_linux) {
+    if (is_nacl && !is_nacl_saigo) {
       # This is for the pnacl_newlib toolchain. It's only used to build
       # a few independent ppapi test files that don't pull in any other
       # dependencies.

components/omnibox/browser/autocomplete_result.cc

@@ -968,12 +968,7 @@ void AutocompleteResult::MaybeCullTailSuggestions(
   // as a default match (and that's a non-tail suggestion).
   // 1) above.
   if (default_tail != matches->end() && default_non_tail == matches->end()) {
-    // TODO(thakis): Remove this branch once CFI builds use C++17.
-#if __cplusplus >= 201703L
     base::EraseIf(*matches, std::not_fn(is_tail));
-#else
-    base::EraseIf(*matches, std::not1(is_tail));
-#endif
     return;
   }
   // 2) above.