Remove the MojoChannelAssociatedCrashesOnSendError feature.

Stable experiment demonstrates that SendMessageOnSequence can only fail
if `connector_->encountered_error()` is true, so we make the CHECK no
longer gated by a feature.

Bug: 40944462
Change-Id: Idcbf7e3d209468db1cc8e90d901a6f37f3b65abf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5954810
Commit-Queue: Ken Rockot <rockot@google.com>
Auto-Submit: Francois Pierre Doray <fdoray@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/main@{#1375332}

ipc/ipc_mojo_bootstrap.cc

@@ -23,6 +23,7 @@
 #include "base/memory/ptr_util.h"
 #include "base/memory/raw_ptr.h"
 #include "base/no_destructor.h"
+#include "base/not_fatal_until.h"
 #include "base/ranges/algorithm.h"
 #include "base/sequence_checker.h"
 #include "base/strings/stringprintf.h"
@@ -68,10 +69,6 @@ BASE_FEATURE(kMojoChannelAssociatedSendUsesRunOrPostTask,
              "MojoChannelAssociatedSendUsesRunOrPostTask",
              base::FEATURE_DISABLED_BY_DEFAULT);
 
-BASE_FEATURE(kMojoChannelAssociatedCrashesOnSendError,
-             "MojoChannelAssociatedCrashesOnSendError",
-             base::FEATURE_DISABLED_BY_DEFAULT);
-
 // Used to track some internal Channel state in pursuit of message leaks.
 //
 // TODO(crbug.com/40563310): Remove this.
@@ -918,24 +915,14 @@ class ChannelAssociatedGroupController
       }
       return true;
     }
-    MojoResult result = connector_->AcceptAndGetResult(message);
 
-    // TODO(crbug.com/40944462): Remove this code when the cause of skipped
-    // messages with MojoChannelAssociatedSendUsesRunOrPostTask is understood,
-    // or no later than November 2024.
-    if (result != MOJO_RESULT_OK && !connector_->encountered_error() &&
-        base::FeatureList::IsEnabled(
-            kMojoChannelAssociatedCrashesOnSendError)) {
-      // Crash when sending a message fails and `connector_` can send more
-      // messages, as that breaks the assumption that messages are received in
-      // the order they were sent. Note: `connector_` cannot send more messages
-      // when `encountered_error()` is true.
-      mojo::debug::ScopedMessageErrorCrashKey crash_key(
-          base::StringPrintf("SendMessage failed with error %d", result));
-      CHECK(false);
+    MojoResult result = connector_->AcceptAndGetResult(message);
+    if (result == MOJO_RESULT_OK) {
+      return true;
     }
 
-    return result == MOJO_RESULT_OK;
+    CHECK(connector_->encountered_error(), base::NotFatalUntil::M135);
+    return false;
   }
 
   void SendMessageOnSequenceViaTask(mojo::Message message) {

testing/variations/fieldtrial_testing_config.json

@@ -14165,28 +14165,6 @@
             ]
         }
     ],
-    "MojoChannelAssociatedCrashesOnSendError": [
-        {
-            "platforms": [
-                "android",
-                "android_webview",
-                "chromeos",
-                "chromeos_lacros",
-                "fuchsia",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "MojoChannelAssociatedCrashesOnSendError"
-                    ]
-                }
-            ]
-        }
-    ],
     "MojoChannelAssociatedSendUsesRunOrPostTask": [
         {
             "platforms": [