Use component ImageFetcher instead of iOS one.

ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc

Index: ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
diff --git a/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc b/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
index 2c6a3d1a360a1d039174c0dbba3002a4c474c054..1b1765a480fcd2d48fb5b3afe34eb062dcff326c 100644
--- a/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
+++ b/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
@@ -16,6 +16,7 @@
 #include "components/bookmarks/browser/bookmark_model.h"
 #include "components/image_fetcher/image_decoder.h"
 #include "components/image_fetcher/image_fetcher.h"
+#include "components/image_fetcher/image_fetcher_impl.h"
 #include "components/keyed_service/core/service_access_type.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/ntp_snippets/bookmarks/bookmark_suggestions_provider.h"
@@ -40,7 +41,6 @@
 #include "ios/chrome/browser/history/history_service_factory.h"
 #include "ios/chrome/browser/signin/oauth2_token_service_factory.h"
 #include "ios/chrome/browser/signin/signin_manager_factory.h"
-#include "ios/chrome/browser/suggestions/image_fetcher_impl.h"
 #include "ios/chrome/browser/suggestions/ios_image_decoder_impl.h"
 #include "ios/chrome/common/channel_info.h"
 #include "ios/web/public/browser_state.h"
@@ -49,6 +49,7 @@
 
 using bookmarks::BookmarkModel;
 using history::HistoryService;
+using image_fetcher::ImageFetcherImpl;
 using ios::BookmarkModelFactory;
 using ntp_snippets::BookmarkSuggestionsProvider;
 using ntp_snippets::ContentSuggestionsService;
@@ -59,7 +60,6 @@ using ntp_snippets::RemoteSuggestionsProviderImpl;
 using ntp_snippets::RemoteSuggestionsStatusService;
 using ntp_snippets::SchedulingRemoteSuggestionsProvider;
 using suggestions::CreateIOSImageDecoder;
-using suggestions::ImageFetcherImpl;
 
 namespace {
 
@@ -154,17 +154,20 @@ IOSChromeContentSuggestionsServiceFactory::BuildServiceInstanceFor(
             ->GetSequencedTaskRunnerWithShutdownBehavior(
                 base::SequencedWorkerPool::GetSequenceToken(),
                 base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
+
     auto suggestions_fetcher = base::MakeUnique<RemoteSuggestionsFetcher>(
         signin_manager, token_service, request_context, prefs, nullptr,
         base::Bind(&ParseJson), GetChannel() == version_info::Channel::STABLE
                                     ? google_apis::GetAPIKey()
                                     : google_apis::GetNonStableAPIKey(),
         service->user_classifier());
+
     auto provider = base::MakeUnique<RemoteSuggestionsProviderImpl>(
         service.get(), prefs, GetApplicationContext()->GetApplicationLocale(),
         service->category_ranker(), std::move(suggestions_fetcher),
-        base::MakeUnique<ImageFetcherImpl>(request_context.get(),
-                                           web::WebThread::GetBlockingPool()),
+        base::MakeUnique<ImageFetcherImpl>(
+            CreateIOSImageDecoder(web::WebThread::GetBlockingPool()),

[gambard, 2017/02/17 08:16:09]

I have used the same pool as the one used by the the ImageFetcher I am replacing
but I don't understand why we are not using "task_runner" here, as we do for the
ImageDecoder at line 171.

[noyau (Ping after 24h), 2017/02/17 10:04:18]

Probably historical. The taskrunner is createed on line 152 with the same
blocking pool anyway.

But I'm confused why there is a need for two image decoders? Is it a transient
state while you remove old code?

[Marc Treib, 2017/02/17 10:10:31]

Yup, transient - in fact, we have the same problem (both Fetcher and Decoder) in
other places. Removing the special iOS implementation of ImageFetcherImpl will
allow us to make this all better :)

[gambard, 2017/02/17 10:11:16]

No, the RemoteSuggestionsProviderImpl (living in components/ntp_snippets) takes
an ImageFetcher and an ImageDecoder.
This is because the images fetched are cached in a database, not decoded
(probably to save space). When retrieving them, it needs to decode it.
It can be removed once we remove the iOS implementation.

[Marc Treib, 2017/02/17 10:13:19]

Concurrent comments ftw :D

Some more detail: Once the same ImageFetcherImpl is used everywhere, my plan is
to add a "GetImageDecoder()" on it (since the fetcher contains a decoder
anyway). Then we won't have to pass the decoder in separately.

+            request_context.get()),
         CreateIOSImageDecoder(task_runner),
         base::MakeUnique<RemoteSuggestionsDatabase>(database_dir, task_runner),
         base::MakeUnique<RemoteSuggestionsStatusService>(signin_manager,