TSANv2: disable non sandbox-related threading checks under TSAN.

Allow Chromium to start under TSAN by removing the threading checks
before fork() in that environment.

Note that TSANv2 doesn't reliably support non-spawn fork() for now:
https://code.google.com/p/thread-sanitizer/issues/detail?id=44

But at least this allows using it on Chrome despite risks of running
into deadlocks.

NOTRY=true

Review URL: https://codereview.chromium.org/130423014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247708 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/render_sandbox_host_linux.cc

@@ -709,12 +709,12 @@ void RenderSandboxHostLinux::Init(const std::string& sandbox_path) {
   childs_lifeline_fd_ = pipefds[1];
 
   // We need to be monothreaded before we fork().
-#if !defined(TOOLKIT_GTK)
+#if !defined(TOOLKIT_GTK) && !defined(THREAD_SANITIZER)
   // Exclude gtk port as TestSuite in base/tests/test_suite.cc is calling
   // gtk_init.
   // TODO(oshima): Remove ifdef when above issues are resolved.
   DCHECK_EQ(1, base::GetNumberOfThreads(base::GetCurrentProcessHandle()));
-#endif
+#endif  // !defined(TOOLKIT_GTK) && !defined(THREAD_SANITIZER)
   pid_ = fork();
   if (pid_ == 0) {
     if (IGNORE_EINTR(close(fds[0])) < 0)

content/zygote/zygote_main_linux.cc

@@ -332,7 +332,9 @@ static bool EnterSuidSandbox(LinuxSandbox* linux_sandbox,
   PreSandboxInit();
 
   // Check that the pre-sandbox initialization didn't spawn threads.
+#if !defined(THREAD_SANITIZER)
   DCHECK(linux_sandbox->IsSingleThreaded());
+#endif
 
   if (setuid_sandbox->IsSuidSandboxChild()) {
     // Use the SUID sandbox.  This still allows the seccomp sandbox to