CacheStorage: Remove CacheStorageSequence feature and virtual test suite.

This feature launched to 100% on windows, mac, and android in M80.  It
was just enabled by default on ChromeOS in ToT after an extended period
investigating performance regressions.

Bug: 960012
Change-Id: I6e1edacd5f3c180f64a024cb948022aeaf130d1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450495Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813905}

content/browser/cache_storage/cache_storage_context_impl.cc

@@ -5,7 +5,6 @@
 #include "content/browser/cache_storage/cache_storage_context_impl.h"
 
 #include "base/bind.h"
-#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/sequenced_task_runner.h"
 #include "base/task/thread_pool.h"
@@ -28,12 +27,7 @@ namespace content {
 
 namespace {
 
-const base::Feature kCacheStorageSequenceFeature{
-    "CacheStorageSequence", base::FEATURE_ENABLED_BY_DEFAULT};
-
 scoped_refptr<base::SequencedTaskRunner> CreateSchedulerTaskRunner() {
-  if (!base::FeatureList::IsEnabled(kCacheStorageSequenceFeature))
-    return GetIOThreadTaskRunner({});
   return base::ThreadPool::CreateSequencedTaskRunner(
       {base::TaskPriority::USER_VISIBLE});
 }

testing/variations/fieldtrial_testing_config.json

@@ -1248,25 +1248,6 @@
             ]
         }
     ],
-    "CacheStorageSequenceChromeOS": [
-        {
-            "platforms": [
-                "chromeos"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled6_v7",
-                    "params": {
-                        "min": "6"
-                    },
-                    "enable_features": [
-                        "BrowserThreadPoolAdjustment",
-                        "CacheStorageSequence"
-                    ]
-                }
-            ]
-        }
-    ],
     "CastMediaRouteProviderAndGlobalMediaControlsForCast": [
         {
             "platforms": [

third_party/blink/web_tests/FlagExpectations/enable-blink-features=ForceSynchronousHTMLParsing

@@ -8,9 +8,6 @@
 ### external/wpt/service-workers/service-worker/
 crbug.com/901056 external/wpt/service-workers/service-worker/xhr-response-url.https.html [ Crash ]
 
-### virtual/cache-storage-sequence/external/wpt/service-workers/service-worker/
-crbug.com/901056 virtual/cache-storage-sequence/external/wpt/service-workers/service-worker/xhr-response-url.https.html [ Crash ]
-
 ### virtual/omt-worker-fetch/external/wpt/service-workers/service-worker/
 crbug.com/901056 virtual/omt-worker-fetch/external/wpt/service-workers/service-worker/xhr-response-url.https.html [ Crash ]
 

third_party/blink/web_tests/VirtualTestSuites

@@ -582,11 +582,6 @@
     "bases": ["http/tests/payments/payment-request-app-store-billing-mandatory-total.html"],
     "args": ["--disable-blink-features=PaymentRequestTotalOptional"]
   },
-  {
-    "prefix": "cache-storage-sequence",
-    "bases": ["external/wpt/service-workers"],
-    "args": ["--enable-features=CacheStorageSequence"]
-  },
   {
     "prefix": "conditional-appcache-delay",
     "bases": ["http/tests/loading/appcache-delay"],

third_party/blink/web_tests/virtual/cache-storage-sequence/external/wpt/service-workers/README.txt

-This suite runs the ServiceWorker and CacheStorage tests with the
-CacheStorageSequence feature enabled.  This makes CacheStorage operate on
-the IO thread in the browser process.