Remove trap handler fallback for sanitizers

Since https://crrev.com/c/1335572, our sanitizers allow to set custom
segfault handlers. Thus remove special code that was added to handle
sanitizers that prevent installation of segfault handlers. Instead,
CHECK that the signal handler was installed correctly.

R=ahaas@chromium.org, mseaborn@chromium.org, mark@chromium.org

Bug: chromium:830894
Change-Id: I3bd66e33efdceb3e8469f3f4a09fbde90cb3d7ec
Reviewed-on: https://chromium-review.googlesource.com/c/1392199Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58513}

src/trap-handler/handler-outside-posix.cc

@@ -13,7 +13,7 @@
 //    should be as self-contained as possible to make it easy to audit the code.
 //
 // 2. Any changes must be reviewed by someone from the crash reporting
-//    or security team. Se OWNERS for suggested reviewers.
+//    or security team. See OWNERS for suggested reviewers.
 //
 // For more information, see https://goo.gl/yMeyUY.
 //
@@ -52,36 +52,21 @@ bool RegisterDefaultTrapHandler() {
     return false;
   }
 
-// Sanitizers often prevent us from installing our own signal handler. Attempt
-// to detect this and if so, refuse to enable trap handling.
-//
-// TODO(chromium:830894): Remove this once all bots support custom signal
-// handlers.
-#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
-    defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER) ||    \
-    defined(UNDEFINED_SANITIZER)
+  // Check that the signal handler is indeed registered. Sanitizers for example
+  // might prevent this, and then report crashes later because signals are not
+  // being caught correctly.
   struct sigaction installed_handler;
   CHECK_EQ(sigaction(kOobSignal, NULL, &installed_handler), 0);
-  // If the installed handler does not point to HandleSignal, then
-  // allow_user_segv_handler is 0.
-  if (installed_handler.sa_sigaction != HandleSignal) {
-    printf(
-        "WARNING: sanitizers are preventing signal handler installation. "
-        "Trap handlers are disabled.\n");
-    return false;
-  }
-#endif
+  CHECK_EQ(HandleSignal, installed_handler.sa_sigaction);
 
   g_is_default_signal_handler_registered = true;
   return true;
 }
 
 void RemoveTrapHandler() {
-  if (g_is_default_signal_handler_registered) {
-    if (sigaction(kOobSignal, &g_old_handler, nullptr) == 0) {
-      g_is_default_signal_handler_registered = false;
-    }
-  }
+  if (!g_is_default_signal_handler_registered) return;
+  if (sigaction(kOobSignal, &g_old_handler, nullptr) != 0) return;
+  g_is_default_signal_handler_registered = false;
 }
 #endif  // V8_TRAP_HANDLER_SUPPORTED