[translate] Fix shutdown race for translate ranker model loader.

components/translate/core/browser/translate_url_fetcher.cc

Index: components/translate/core/browser/translate_url_fetcher.cc
diff --git a/components/translate/core/browser/translate_url_fetcher.cc b/components/translate/core/browser/translate_url_fetcher.cc
index dbbff3176056f9c9c199a3e1e7c84e4503213316..296fa283c775b2d2f83db6a1f591413157a42670 100644
--- a/components/translate/core/browser/translate_url_fetcher.cc
+++ b/components/translate/core/browser/translate_url_fetcher.cc
@@ -46,13 +46,22 @@ bool TranslateURLFetcher::Request(
   url_ = url;
   callback_ = callback;
 
+  // If the TranslateDownloadManager's request context getter is nullptr then
+  // shutdown is in progress. Abort the request, which can't proceed with a
+  // null request_context_getter.
+  net::URLRequestContextGetter* request_context_getter =
+      TranslateDownloadManager::GetInstance()->request_context();

[groby-ooo-7-16, 2017/04/24 19:12:46]

So, request_context is RefCountedThreadSafe. Should we maybe return a
scoped_refptr? Or at least take the parameter into a scoped_refptr?

[Roger McFarlane (Chromium), 2017/04/24 20:31:34]

I put the returned value in to a scoped_refptr.

It's a bit unfortunate that the getter and setter take raw pointer values. But I
suspect it might be because taking and returning scoped_refptr<T> by value
requires that the full definition of T be available, which means you can't just
forward declare T.

I'm not averse to changing it to accept/return scoped_refptr instead, but that's
probably be better done in its own CL.

+  if (request_context_getter == nullptr)
+    return false;
+
+  // Create and initialize the URL fetcher.
   fetcher_ = net::URLFetcher::Create(id_, url_, net::URLFetcher::GET, this);
   data_use_measurement::DataUseUserData::AttachToFetcher(
       fetcher_.get(), data_use_measurement::DataUseUserData::TRANSLATE);
   fetcher_->SetLoadFlags(net::LOAD_DO_NOT_SEND_COOKIES |
                          net::LOAD_DO_NOT_SAVE_COOKIES);
-  fetcher_->SetRequestContext(
-      TranslateDownloadManager::GetInstance()->request_context());
+  fetcher_->SetRequestContext(request_context_getter);
+
   // Set retry parameter for HTTP status code 5xx. This doesn't work against
   // 106 (net::ERR_INTERNET_DISCONNECTED) and so on.
   // TranslateLanguageList handles network status, and implements retry.