mojo: Use a more appripriate task runner at HandleSignalTracker's SimpleWatch

HandleSignalTracker's SimpleWatcher objects always used the default task
runner. This CL fixes this by passing a more appropriate task runner
obtained from Connector.

Bug: 870606
Change-Id: Ib9028175d224b7768606ac1b2319662bd9700f37
Reviewed-on: https://chromium-review.googlesource.com/c/1328550Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607147}

mojo/public/cpp/bindings/lib/connector.cc

@@ -401,8 +401,8 @@ void Connector::WaitToReadMore() {
       base::Bind(&Connector::OnWatcherHandleReady, base::Unretained(this)));
 
   if (message_pipe_.is_valid()) {
-    peer_remoteness_tracker_.emplace(message_pipe_.get(),
-                                     MOJO_HANDLE_SIGNAL_PEER_REMOTE);
+    peer_remoteness_tracker_.emplace(
+        message_pipe_.get(), MOJO_HANDLE_SIGNAL_PEER_REMOTE, task_runner_);
   }
 
   if (rv != MOJO_RESULT_OK) {

mojo/public/cpp/system/handle_signal_tracker.cc

@@ -9,14 +9,16 @@
 
 namespace mojo {
 
-HandleSignalTracker::HandleSignalTracker(Handle handle,
-                                         MojoHandleSignals signals)
+HandleSignalTracker::HandleSignalTracker(
+    Handle handle,
+    MojoHandleSignals signals,
+    scoped_refptr<base::SequencedTaskRunner> task_runner)
     : high_watcher_(FROM_HERE,
                     SimpleWatcher::ArmingPolicy::MANUAL,
-                    base::SequencedTaskRunnerHandle::Get()),
+                    task_runner),
       low_watcher_(FROM_HERE,
                    SimpleWatcher::ArmingPolicy::MANUAL,
-                   base::SequencedTaskRunnerHandle::Get()) {
+                   std::move(task_runner)) {
   MojoResult rv = high_watcher_.Watch(
       handle, signals, MOJO_TRIGGER_CONDITION_SIGNALS_SATISFIED,
       base::Bind(&HandleSignalTracker::OnNotify, base::Unretained(this)));

mojo/public/cpp/system/handle_signal_tracker.h

@@ -12,6 +12,10 @@
 #include "mojo/public/cpp/system/simple_watcher.h"
 #include "mojo/public/cpp/system/system_export.h"
 
+namespace base {
+class SequencedTaskRunner;
+}
+
 namespace mojo {
 
 // This class helps track the state of specific signal on a handle so that
@@ -29,7 +33,10 @@ class MOJO_CPP_SYSTEM_EXPORT HandleSignalTracker {
 
   // Constructs a tracker which tracks |signals| on |handle|. |signals| may
   // be any single signal flag or any combination of signal flags.
-  HandleSignalTracker(Handle handle, MojoHandleSignals signals);
+  HandleSignalTracker(Handle handle,
+                      MojoHandleSignals signals,
+                      scoped_refptr<base::SequencedTaskRunner> task_runner =
+                          base::SequencedTaskRunnerHandle::Get());
   ~HandleSignalTracker();
 
   const HandleSignalsState& last_known_state() const {