Remove shadow stack references

Remove references to shadow stacks from the profiling documentation and
from the shutdown signal handler.
The only remaining references are in the old tcmalloc implementation, which
will eventually be removed.

BUG=724399,b:70905156

Change-Id: I2b1a854dc2eb081ec9bfb5401fc2c5ebd1860c4e
Reviewed-on: https://chromium-review.googlesource.com/1239442Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Alexander Potapenko <glider@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Gabriel Marin <gmx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593639}

chrome/app/shutdown_signal_handlers_posix.cc

@@ -183,12 +183,11 @@ void InstallShutdownSignalHandlers(
   g_pipe_pid = getpid();
   g_shutdown_pipe_read_fd = pipefd[0];
   g_shutdown_pipe_write_fd = pipefd[1];
-#if !defined(ADDRESS_SANITIZER) && !defined(KEEP_SHADOW_STACKS)
+#if !defined(ADDRESS_SANITIZER)
   const size_t kShutdownDetectorThreadStackSize = PTHREAD_STACK_MIN * 2;
 #else
-  // ASan instrumentation and -finstrument-functions (used for keeping the
-  // shadow stacks) bloat the stack frames, so we need to increase the stack
-  // size to avoid hitting the guard page.
+  // ASan instrumentation bloats the stack frames, so we need to increase the
+  // stack size to avoid hitting the guard page.
   const size_t kShutdownDetectorThreadStackSize = PTHREAD_STACK_MIN * 4;
 #endif
   ShutdownDetector* detector = new ShutdownDetector(