[blink] Migrate worker_pool:: interface away from base::ThreadPool()-as-a-trait

base::ThreadPool:: (API as a destination) is the new desired paradigm.

worker_pool:: was already API-as-destination; can remove redundant
ThreadPool() trait with new API.

R=haraken@chromium.org

Bug: 1026641
Change-Id: Ida08feab710143da2308ef1361550a9aced39d2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2105454
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750565}

third_party/blink/renderer/bindings/core/v8/script_streamer.cc

@@ -501,8 +501,7 @@ bool ScriptStreamer::TryStartStreaming(
   // they wait for more input.
   // TODO(leszeks): Decrease the priority of these tasks where possible.
   worker_pool::PostTask(
-      FROM_HERE,
-      {base::ThreadPool(), base::TaskPriority::USER_BLOCKING, base::MayBlock()},
+      FROM_HERE, {base::TaskPriority::USER_BLOCKING, base::MayBlock()},
       CrossThreadBindOnce(RunScriptStreamingTask,
                           WTF::Passed(std::move(script_streaming_task)),
                           WrapCrossThreadPersistent(this),

third_party/blink/renderer/modules/mediastream/media_stream_audio_processor.cc

@@ -368,8 +368,7 @@ void MediaStreamAudioProcessor::OnStartDump(base::File dump_file) {
   } else {
     // Post the file close to avoid blocking the main thread.
     worker_pool::PostTask(
-        FROM_HERE,
-        {base::ThreadPool(), base::TaskPriority::LOWEST, base::MayBlock()},
+        FROM_HERE, {base::TaskPriority::LOWEST, base::MayBlock()},
         CrossThreadBindOnce([](base::File) {}, std::move(dump_file)));
   }
 }

third_party/blink/renderer/platform/mediastream/audio_service_audio_processor_proxy.cc

@@ -62,8 +62,7 @@ void AudioServiceAudioProcessorProxy::OnStartDump(base::File dump_file) {
   } else {
     // Post the file close to avoid blocking the main thread.
     worker_pool::PostTask(
-        FROM_HERE,
-        {base::ThreadPool(), base::TaskPriority::LOWEST, base::MayBlock()},
+        FROM_HERE, {base::TaskPriority::LOWEST, base::MayBlock()},
         CrossThreadBindOnce([](base::File) {}, std::move(dump_file)));
   }
 }

third_party/blink/renderer/platform/scheduler/common/worker_pool.cc

@@ -5,23 +5,21 @@
 #include "third_party/blink/renderer/platform/scheduler/public/worker_pool.h"
 
 #include "base/location.h"
-#include "base/task/post_task.h"
+#include "base/task/thread_pool.h"
 
 namespace blink {
 
 namespace worker_pool {
 
 void PostTask(const base::Location& location, CrossThreadOnceClosure closure) {
-  PostTask(
-      location,
-      {base::ThreadPool(), base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
+  PostTask(location, {base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
            std::move(closure));
 }
 
 void PostTask(const base::Location& location,
               const base::TaskTraits& traits,
               CrossThreadOnceClosure closure) {
-  base::PostTask(location, traits,
+  base::ThreadPool::PostTask(location, traits,
                              ConvertToBaseOnceCallback(std::move(closure)));
 }
 

third_party/blink/renderer/platform/scheduler/public/worker_pool.h

@@ -15,9 +15,9 @@ namespace blink {
 
 namespace worker_pool {
 
-// These are a thin wrapper around base::ThreadPoolInstance to ensure that all
-// callers use CrossThreadBindOnce instead of base::Bind to ensure that
-// all non-thread-safe objects are copied properly.
+// These are a thin wrapper around base::ThreadPool to ensure that all callers
+// use CrossThreadBindOnce instead of base::Bind to ensure that all
+// non-thread-safe objects are copied properly.
 //
 // All tasks that do not care about which thread they are running on
 // (e.g. compressing/uncompressing tasks) use this API.