Remove calls to IsRunningSequenceOnCurrentThread() from crash_handler_host_linux.cc

SequencedWorkerPool is being migrated to base/task_scheduler and there
is no equivalent to IsRunningSequenceOnCurrentThread() in
base/task_scheduler.

Developers should use SequenceChecker to verify that tasks run
sequentially. Unlike
SequencedWorkerPool::IsRunningSequenceOnCurrentThread(),
SequenceChecker works everywhere in Chrome (MessageLoop,
SequencedWorkerPool, base/task_scheduler...).

BUG=622400

Review-Url: https://codereview.chromium.org/2318123002
Cr-Commit-Position: refs/heads/master@{#417388}

components/crash/content/browser/crash_handler_host_linux.cc

@@ -101,6 +101,8 @@ CrashHandlerHostLinux::CrashHandlerHostLinux(const std::string& process_type,
 #endif
       shutting_down_(false),
       worker_pool_token_(base::SequencedWorkerPool::GetSequenceToken()) {
+  write_dump_file_sequence_checker_.DetachFromSequence();
+
   int fds[2];
   // We use SOCK_SEQPACKET rather than SOCK_DGRAM to prevent the process from
   // sending datagrams to other sockets on the system. The sandbox may prevent
@@ -401,8 +403,7 @@ void CrashHandlerHostLinux::WriteDumpFile(std::unique_ptr<BreakpadInfo> info,
                                           std::unique_ptr<char[]> crash_context,
                                           pid_t crashing_pid,
                                           int signal_fd) {
-  DCHECK(BrowserThread::GetBlockingPool()->IsRunningSequenceOnCurrentThread(
-      worker_pool_token_));
+  DCHECK(write_dump_file_sequence_checker_.CalledOnValidSequence());
 
   // Set |info->distro| here because base::GetLinuxDistro() needs to run on a
   // blocking thread.

components/crash/content/browser/crash_handler_host_linux.h

@@ -14,6 +14,7 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
+#include "base/sequence_checker.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "components/crash/content/app/breakpad_linux_impl.h"
 
@@ -102,6 +103,9 @@ class CrashHandlerHostLinux : public base::MessageLoopForIO::Watcher,
   // by other tasks.
   base::SequencedWorkerPool::SequenceToken worker_pool_token_;
 
+  // Used to verify that calls to WriteDumpFile() are sequenced.
+  base::SequenceChecker write_dump_file_sequence_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(CrashHandlerHostLinux);
 };