Revert "[flags] Skip --random-seed in FlagList::Hash"

This reverts commit 9fe53c4f.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20isolates/17044/overview

Original change's description:
> [flags] Skip --random-seed in FlagList::Hash
>
> Node and friends use --random-seed to temporary reset the seed for
> predictable code-cache creation. To allow custom random seeds at runtime
> the flag is reset for encoding the FlagList::Hash in the snapshots.
>
> We will soon disallow changing flags via the API after V8 has been
> initialized. In order to make node work we will exclude --random-seed
> from the FlagList::Hash calculation.
>
> Drive-by-fix:
> * Lazily initialize flag_hash instead of calculating it after every call
>   to SetFlagsFromString / EnforceFlagImplications.
> * Simplify hash string source creation since out << flag now includes
>   the full flag information
>
> Bug: v8:12309
> Change-Id: I1a168f4702d8c4d160ff12fdbea881731e4ea8b6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3218159
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#77345}

Bug: v8:12309
Change-Id: I5e431c3e3ccccaab2ef7aa025b51d42f837f08b9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3218979Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#77347}

src/flags/flags.cc

@@ -796,16 +796,23 @@ static uint32_t flag_hash = 0;
 
 void ComputeFlagListHash() {
   std::ostringstream modified_args_as_string;
-  if (COMPRESS_POINTERS_BOOL) modified_args_as_string << "ptr-compr";
-  if (DEBUG_BOOL) modified_args_as_string << "debug";
-  for (const Flag& flag : flags) {
-    if (flag.IsDefault()) continue;
-    // We want to be able to flip --profile-deserialization without
-    // causing the code cache to get invalidated by this hash.
-    if (flag.PointsTo(&FLAG_profile_deserialization)) continue;
-    // Skip FLAG_random_seed to allow predictable code caching.
-    if (flag.PointsTo(&FLAG_random_seed)) continue;
-    modified_args_as_string << flag;
+  if (COMPRESS_POINTERS_BOOL) {
+    modified_args_as_string << "ptr-compr";
+  }
+  if (DEBUG_BOOL) {
+    modified_args_as_string << "debug";
+  }
+  for (size_t i = 0; i < num_flags; ++i) {
+    Flag* current = &flags[i];
+    if (current->PointsTo(&FLAG_profile_deserialization)) {
+      // We want to be able to flip --profile-deserialization without
+      // causing the code cache to get invalidated by this hash.
+      continue;
+    }
+    if (!current->IsDefault()) {
+      modified_args_as_string << i;
+      modified_args_as_string << *current;
+    }
   }
   std::string args(modified_args_as_string.str());
   flag_hash = static_cast<uint32_t>(
@@ -830,7 +837,6 @@ bool TriggerImplication(bool premise, const char* premise_name,
 
 // static
 void FlagList::EnforceFlagImplications() {
-  flag_hash = 0;
   bool changed;
   do {
     changed = false;
@@ -838,14 +844,10 @@ void FlagList::EnforceFlagImplications() {
 #include "src/flags/flag-definitions.h"  // NOLINT(build/include)
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
   } while (changed);
+  ComputeFlagListHash();
 }
 
-uint32_t FlagList::Hash() {
-  if (flag_hash == 0) {
-    ComputeFlagListHash();
-  }
-  return flag_hash;
-}
+uint32_t FlagList::Hash() { return flag_hash; }
 
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS