Remove MessageLoop::current() from ppapi/proxy.

Whenever possible, use ThreadTaskRunnerHandle::Get() instead of
MessageLoop::current(). ThreadTaskRunnerHandle::Get() works within
TaskScheduler while MessageLoop::current() doesn't.

Good reasons to use MessageLoop::current():
- Add destruction, nesting or task observers.
- Run nested loops.

Bad reasons to use MessageLoop::current():
- Post tasks. Use ThreadTaskRunnerHandle::Get() instead.
- Watch a file descriptor. Use FileDescriptorWatcher instead.
- Verify that it is possible to post tasks to the current thread.
  Use ThreadTaskRunnerHandle::IsSet() instead.
- Verify that code runs on a specific thread. Use
  SingleThreadTaskRunner::BelongsToCurrentThread() instead.

BUG=650723

Review-Url: https://codereview.chromium.org/2407393002
Cr-Commit-Position: refs/heads/master@{#424863}

ppapi/proxy/plugin_globals.cc

@@ -4,11 +4,10 @@
 
 #include "ppapi/proxy/plugin_globals.h"
 
-#include "base/location.h"
 #include "base/macros.h"
-#include "base/single_thread_task_runner.h"
 #include "base/task_runner.h"
 #include "base/threading/thread.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_sender.h"
 #include "ppapi/proxy/plugin_dispatcher.h"
@@ -189,7 +188,7 @@ base::TaskRunner* PluginGlobals::GetFileTaskRunner() {
 void PluginGlobals::MarkPluginIsActive() {
   if (!plugin_recently_active_) {
     plugin_recently_active_ = true;
-    if (!GetBrowserSender() || !base::MessageLoop::current())
+    if (!GetBrowserSender() || !base::ThreadTaskRunnerHandle::IsSet())
       return;
     GetBrowserSender()->Send(new PpapiHostMsg_Keepalive());
     DCHECK(keepalive_throttle_interval_milliseconds_);

ppapi/proxy/proxy_completion_callback_factory.h

@@ -8,7 +8,7 @@
 #include <stdint.h>
 
 #include "base/logging.h"
-#include "base/message_loop/message_loop.h"
+#include "base/sequence_checker.h"
 #include "ppapi/cpp/completion_callback.h"
 #include "ppapi/utility/completion_callback_factory.h"
 
@@ -21,38 +21,26 @@ class ProxyNonThreadSafeThreadTraits {
  public:
   class RefCount {
    public:
-    RefCount() : ref_(0) {
-#ifndef NDEBUG
-      message_loop_ = base::MessageLoop::current();
-#endif
-    }
+    RefCount() : ref_(0) {}
 
     ~RefCount() {
-#ifndef NDEBUG
-      DCHECK(message_loop_ == base::MessageLoop::current());
-#endif
+      DCHECK(sequence_checker_.CalledOnValidSequence());
     }
 
     int32_t AddRef() {
-#ifndef NDEBUG
-      DCHECK(message_loop_ == base::MessageLoop::current());
-#endif
+      DCHECK(sequence_checker_.CalledOnValidSequence());
       return ++ref_;
     }
 
     int32_t Release() {
-#ifndef NDEBUG
-      DCHECK(message_loop_ == base::MessageLoop::current());
-#endif
+      DCHECK(sequence_checker_.CalledOnValidSequence());
       DCHECK(ref_ > 0);
       return --ref_;
     }
 
    private:
     int32_t ref_;
-#ifndef NDEBUG
-    base::MessageLoop* message_loop_;
-#endif
+    base::SequenceChecker sequence_checker_;
   };
 
   // No-op lock class.