Fix ProcessHost shutdown when ProcessHostOnUI is turned on.

It turns out BrowserProcessSubThread is only used for IO thread at this point so it doesn't get a chance to clean up things that live on the UI thread. In a subsequent cl I'll rename it to BrowserProcessIOThread to make it clear, but this is the minmal fix for ProcessHostOnUI for now.

This fixes the remaining failures on the windows bots, which were the InProcessGpuTest tests.

Bug: 904556
Change-Id: Ie3575ecef4d4f206b23b583fbb86c4e6b30f523a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2877684
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Auto-Submit: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#880129}

content/browser/browser_main_loop.cc

@@ -1044,6 +1044,9 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
   if (RenderProcessHost::run_renderer_in_process())
     RenderProcessHostImpl::ShutDownInProcessRenderer();
 
+  if (base::FeatureList::IsEnabled(features::kProcessHostOnUI))
+    BrowserProcessSubThread::ProcessHostCleanUp();
+
   if (parts_) {
     TRACE_EVENT0("shutdown",
                  "BrowserMainLoop::Subsystem:PostMainMessageLoopRun");

content/browser/browser_process_sub_thread.cc

@@ -115,11 +115,6 @@ void BrowserProcessSubThread::CleanUp() {
       ProcessHostCleanUp();
   }
 
-  if (base::FeatureList::IsEnabled(features::kProcessHostOnUI) &&
-      BrowserThread::CurrentlyOn(BrowserThread::UI)) {
-    ProcessHostCleanUp();
-  }
-
   notification_service_.reset();
 
 #if defined(OS_WIN)

content/browser/browser_process_sub_thread.h

@@ -53,6 +53,8 @@ class CONTENT_EXPORT BrowserProcessSubThread : public base::Thread {
   // starting this BrowserProcessSubThread.
   void AllowBlockingForTesting();
 
+  static void ProcessHostCleanUp();
+
  protected:
   void Init() override;
   void Run(base::RunLoop* run_loop) override;
@@ -71,8 +73,6 @@ class CONTENT_EXPORT BrowserProcessSubThread : public base::Thread {
   // This method encapsulates cleanup that needs to happen on the IO thread.
   void IOThreadCleanUp();
 
-  void ProcessHostCleanUp();
-
   const BrowserThread::ID identifier_;
 
   // BrowserThreads are not allowed to do file I/O nor wait on synchronization