Bind TwoPhaseUploader to a sequence, not a thread.

chrome/browser/safe_browsing/two_phase_uploader.cc

Index: chrome/browser/safe_browsing/two_phase_uploader.cc
diff --git a/chrome/browser/safe_browsing/two_phase_uploader.cc b/chrome/browser/safe_browsing/two_phase_uploader.cc
index 07fd70a4ee80cf56aaa1087634a8b4b146c7b195..d5652ff8d6e73ebfbcf1e69e05bb487ca01bcfcc 100644
--- a/chrome/browser/safe_browsing/two_phase_uploader.cc
+++ b/chrome/browser/safe_browsing/two_phase_uploader.cc
@@ -11,9 +11,9 @@
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/sequence_checker.h"
 #include "base/task_runner.h"
 #include "components/data_use_measurement/core/data_use_user_data.h"
-#include "content/public/browser/browser_thread.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_fetcher.h"
@@ -42,7 +42,7 @@ class TwoPhaseUploaderImpl : public net::URLFetcherDelegate,
       const ProgressCallback& progress_callback,
       const FinishCallback& finish_callback,
       const net::NetworkTrafficAnnotationTag& traffic_annotation);
-  ~TwoPhaseUploaderImpl() override;
+  ~TwoPhaseUploaderImpl() override = default;
 
   // Begins the upload process.
   void Start() override;
@@ -71,6 +71,10 @@ class TwoPhaseUploaderImpl : public net::URLFetcherDelegate,
 
   std::unique_ptr<net::URLFetcher> url_fetcher_;
 
+  // Ensure access to the state_ variable is sequenced, and that callbacks are
+  // invoked on the same sequence as Start.
+  base::SequenceChecker sequence_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(TwoPhaseUploaderImpl);
 };
 
@@ -92,22 +96,22 @@ TwoPhaseUploaderImpl::TwoPhaseUploaderImpl(
       progress_callback_(progress_callback),
       finish_callback_(finish_callback),
       traffic_annotation_(traffic_annotation) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-}
-
-TwoPhaseUploaderImpl::~TwoPhaseUploaderImpl() {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  // The callbacks must be invoked on the same sequence as Start, but that
+  // doesn't need to be the same sequence the TwoPhaseUploaderImpl was
+  // constructed on.
+  sequence_checker_.DetachFromSequence();
 }
 
 void TwoPhaseUploaderImpl::Start() {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  // Bind the sequence checker to the current sequence.
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   DCHECK_EQ(STATE_NONE, state_);
 
   UploadMetadata();
 }
 
 void TwoPhaseUploaderImpl::OnURLFetchComplete(const net::URLFetcher* source) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   net::URLRequestStatus status = source->GetStatus();
   int response_code = source->GetResponseCode();
 
@@ -163,7 +167,7 @@ void TwoPhaseUploaderImpl::OnURLFetchUploadProgress(
     const net::URLFetcher* source,
     int64_t current,
     int64_t total) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   DVLOG(3) << __func__ << " " << source->GetURL().spec() << " " << current
            << "/" << total;
   if (state_ == UPLOAD_FILE && !progress_callback_.is_null())
@@ -171,7 +175,7 @@ void TwoPhaseUploaderImpl::OnURLFetchUploadProgress(
 }
 
 void TwoPhaseUploaderImpl::UploadMetadata() {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   state_ = UPLOAD_METADATA;
   url_fetcher_ = net::URLFetcher::Create(base_url_, net::URLFetcher::POST, this,
                                          traffic_annotation_);
@@ -185,7 +189,7 @@ void TwoPhaseUploaderImpl::UploadMetadata() {
 }
 
 void TwoPhaseUploaderImpl::UploadFile() {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   state_ = UPLOAD_FILE;
 
   url_fetcher_ = net::URLFetcher::Create(upload_url_, net::URLFetcher::PUT,
@@ -202,7 +206,7 @@ void TwoPhaseUploaderImpl::UploadFile() {
 void TwoPhaseUploaderImpl::Finish(int net_error,
                                   int response_code,
                                   const std::string& response) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  DCHECK(sequence_checker_.CalledOnValidSequence());
   finish_callback_.Run(state_, net_error, response_code, response);
 }