Migrate remaining NOTREACHED()s in components/

NOTREACHED() and NOTREACHED_IN_MIGRATION() are both CHECK-fatal now.
The former is [[noreturn]] so this CL also performs dead-code removal
after the NOTREACHED().

This CL does not attempt to do additional rewrites of any surrounding
code, like:

if (!foo) {
  NOTREACHED();
}

to CHECK(foo);

Those transforms take a non-trivial amount of time (and there are
thousands of instances). Cleanup can be left as an exercise for the
reader.

Bug: 40580068
Change-Id: I72205fb77747957c6bf33dbea93656fd20085a42
Low-Coverage-Reason: OTHER Should-be-unreachable code
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6010008
Reviewed-by: Rick Byers <rbyers@chromium.org>
Owners-Override: Rick Byers <rbyers@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1382618}

components/prefs/json_pref_store.cc

@@ -471,8 +471,7 @@ void JsonPrefStore::OnFileRead(std::unique_ptr<ReadResult> read_result) {
         // can't complete synchronously, it should never be returned by the read
         // operation itself.
       case PREF_READ_ERROR_MAX_ENUM:
-        NOTREACHED_IN_MIGRATION();
-        break;
+        NOTREACHED();
     }
   }
 

components/prefs/pref_change_registrar.cc

@@ -44,8 +44,7 @@ void PrefChangeRegistrar::Add(std::string_view path,
 void PrefChangeRegistrar::Add(std::string_view path,
                               const NamedChangeCallback& obs) {
   if (!service_) {
-    NOTREACHED_IN_MIGRATION();
-    return;
+    NOTREACHED();
   }
   DCHECK(!IsObserved(path)) << "Already had pref, \"" << path
                             << "\", registered.";

components/prefs/pref_service.cc

@@ -364,8 +364,7 @@ const base::Value* PrefService::GetUserPrefValue(std::string_view path) const {
 
   const Preference* pref = FindPreference(path);
   if (!pref) {
-    NOTREACHED_IN_MIGRATION() << "Trying to get an unregistered pref: " << path;
-    return nullptr;
+    NOTREACHED() << "Trying to get an unregistered pref: " << path;
   }
 
   // Look for an existing preference in the user store. If it doesn't
@@ -420,9 +419,7 @@ void PrefService::ClearPref(std::string_view path) {
 
   const Preference* pref = FindPreference(path);
   if (!pref) {
-    NOTREACHED_IN_MIGRATION()
-        << "Trying to clear an unregistered pref: " << path;
-    return;
+    NOTREACHED() << "Trying to clear an unregistered pref: " << path;
   }
   user_pref_store_->RemoveValue(path, GetWriteFlags(pref));
 }
@@ -544,8 +541,7 @@ base::Value* PrefService::GetMutableUserPref(std::string_view path,
     return nullptr;
   }
   if (pref->GetType() != type) {
-    NOTREACHED_IN_MIGRATION() << "Wrong type for GetMutableValue: " << path;
-    return nullptr;
+    NOTREACHED() << "Wrong type for GetMutableValue: " << path;
   }
 
   // Look for an existing preference in the user store. Return it in case it
@@ -590,10 +586,8 @@ void PrefService::SetUserPrefValue(std::string_view path,
     return;
   }
   if (pref->GetType() != new_value.type()) {
-    NOTREACHED_IN_MIGRATION()
-        << "Trying to set pref " << path << " of type " << pref->GetType()
-        << " to value of type " << new_value.type();
-    return;
+    NOTREACHED() << "Trying to set pref " << path << " of type "
+                 << pref->GetType() << " to value of type " << new_value.type();
   }
 
   user_pref_store_->SetValue(path, std::move(new_value), GetWriteFlags(pref));

components/prefs/pref_value_store.cc

@@ -232,8 +232,7 @@ bool PrefValueStore::PrefValueInStoreRange(
     PrefValueStore::PrefStoreType first_checked_store,
     PrefValueStore::PrefStoreType last_checked_store) const {
   if (first_checked_store > last_checked_store) {
-    NOTREACHED_IN_MIGRATION();
-    return false;
+    NOTREACHED();
   }
 
   for (size_t i = first_checked_store;