Task Manager: Speculative crash fix

It's not clear to me why calling base::ThreadTaskRunnerHandle::Get()
from ArcProcessTaskProvider::ScheduleNextRequest() would fail,
especially since this is happening on the UI thread. But I added a few
things that may fix the issue:
- I noticed that ArcProcessService dtor may be called, but we did't
  stop observing the ProcessSnapshotServer.
- When the task manager is closed, let's invalidate all the weak_ptrs of
  ArcProcessTaskProvider, so we don't get any pending requested from
  ArcProcessService after that.

BUG=1136378

Change-Id: Icdbc8161e397899a2decd7efac13a39462bb6d71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536812Reviewed-by: Willie Koomson <wvk@google.com>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827898}

chrome/browser/chromeos/arc/process/arc_process_service.cc

@@ -306,6 +306,8 @@ ArcProcessService::ArcProcessService(content::BrowserContext* context,
 
 ArcProcessService::~ArcProcessService() {
   arc_bridge_service_->process()->RemoveObserver(this);
+  if (is_observing_process_snapshot_)
+    ProcessSnapshotServer::Get()->RemoveObserver(this);
 }
 
 // static
@@ -327,6 +329,7 @@ ArcProcessService* ArcProcessService::Get() {
 
 void ArcProcessService::RequestAppProcessList(
     RequestProcessListCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   HandleRequest(
       base::BindOnce(&ArcProcessService::ContinueAppProcessListRequest,
                      base::Unretained(this), std::move(callback)));
@@ -334,6 +337,7 @@ void ArcProcessService::RequestAppProcessList(
 
 void ArcProcessService::RequestSystemProcessList(
     RequestProcessListCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   HandleRequest(
       base::BindOnce(&ArcProcessService::ContinueSystemProcessListRequest,
                      base::Unretained(this), std::move(callback)));
@@ -341,12 +345,14 @@ void ArcProcessService::RequestSystemProcessList(
 
 void ArcProcessService::RequestAppMemoryInfo(
     RequestMemoryInfoCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   HandleRequest(base::BindOnce(&ArcProcessService::ContinueAppMemoryInfoRequest,
                                base::Unretained(this), std::move(callback)));
 }
 
 void ArcProcessService::RequestSystemMemoryInfo(
     RequestMemoryInfoCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   HandleRequest(
       base::BindOnce(&ArcProcessService::ContinueSystemMemoryInfoRequest,
                      base::Unretained(this), std::move(callback)));
@@ -354,6 +360,7 @@ void ArcProcessService::RequestSystemMemoryInfo(
 
 void ArcProcessService::OnProcessSnapshotRefreshed(
     const base::ProcessIterator::ProcessEntries& snapshot) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   cached_process_snapshot_ = snapshot;
   last_process_snapshot_time_ = base::Time::Now();
 
@@ -464,6 +471,7 @@ void ArcProcessService::HandleRequest(base::OnceClosure request) {
 
 void ArcProcessService::ContinueAppProcessListRequest(
     RequestProcessListCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   // Since several services call this class to get information about the ARC
   // process list, it can produce a lot of logspam when the board is ARC-ready
   // but the user has not opted into ARC. This redundant check avoids that
@@ -487,6 +495,7 @@ void ArcProcessService::ContinueAppProcessListRequest(
 
 void ArcProcessService::ContinueSystemProcessListRequest(
     RequestProcessListCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   base::PostTaskAndReplyWithResult(
       task_runner_.get(), FROM_HERE,
       base::BindOnce(&GetArcSystemProcessList, cached_process_snapshot_),
@@ -497,6 +506,7 @@ void ArcProcessService::ContinueSystemProcessListRequest(
 
 void ArcProcessService::ContinueAppMemoryInfoRequest(
     RequestMemoryInfoCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   if (!connection_ready_) {
     std::move(callback).Run({});
     return;
@@ -518,6 +528,7 @@ void ArcProcessService::ContinueAppMemoryInfoRequest(
 
 void ArcProcessService::ContinueSystemMemoryInfoRequest(
     RequestMemoryInfoCallback callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   if (!connection_ready_) {
     std::move(callback).Run({});
     return;

chrome/browser/task_manager/providers/arc/arc_process_task_provider.cc

@@ -134,6 +134,7 @@ void ArcProcessTaskProvider::StartUpdating() {
 
 void ArcProcessTaskProvider::StopUpdating() {
   is_updating_ = false;
+  weak_ptr_factory_.InvalidateWeakPtrs();
   nspid_to_task_.clear();
   nspid_to_sys_task_.clear();
 }

chrome/browser/task_manager/providers/vm/vm_process_task_provider.h

@@ -51,10 +51,6 @@ class VmProcessTaskProvider : public TaskProvider,
   // Map of PIDs to the corresponding Task object for a running VM.
   base::flat_map<base::ProcessId, std::unique_ptr<VmProcessTask>> task_map_;
 
-  // Always keep this the last member of this class to make sure it's the
-  // first thing to be destructed.
-  base::WeakPtrFactory<VmProcessTaskProvider> weak_ptr_factory_{this};
-
   DISALLOW_COPY_AND_ASSIGN(VmProcessTaskProvider);
 };