Let IPC::SyncMessageFilter take advantage of thread-safe Send.

ipc/ipc_sync_message_filter.cc

Index: ipc/ipc_sync_message_filter.cc
diff --git a/ipc/ipc_sync_message_filter.cc b/ipc/ipc_sync_message_filter.cc
index d86835d11973ec5427cd7a461652fc32dbf06ae9..f6d485dd4b77d96ec81ba4395142ecb7750d0179 100644
--- a/ipc/ipc_sync_message_filter.cc
+++ b/ipc/ipc_sync_message_filter.cc
@@ -15,17 +15,14 @@
 
 namespace IPC {
 
-SyncMessageFilter::SyncMessageFilter(base::WaitableEvent* shutdown_event)
-    : sender_(NULL),
-      listener_task_runner_(base::ThreadTaskRunnerHandle::Get()),
-      shutdown_event_(shutdown_event) {
-}
-
 bool SyncMessageFilter::Send(Message* message) {
   if (!message->is_sync()) {
     {
       base::AutoLock auto_lock(lock_);
-      if (!io_task_runner_.get()) {
+      if (sender_ && is_channel_send_thread_safe_) {
+        sender_->Send(message);

[michaeln, 2015/08/05 01:46:15]

Nice solution to that ordering problem!

+        return true;
+      } else if (!io_task_runner_.get()) {
         pending_messages_.push_back(message);
         return true;
       }
@@ -112,6 +109,14 @@ bool SyncMessageFilter::OnMessageReceived(const Message& message) {
   return false;
 }
 
+SyncMessageFilter::SyncMessageFilter(base::WaitableEvent* shutdown_event,
+                                     bool is_channel_send_thread_safe)
+    : sender_(NULL),
+      is_channel_send_thread_safe_(is_channel_send_thread_safe),
+      listener_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      shutdown_event_(shutdown_event) {
+}
+
 SyncMessageFilter::~SyncMessageFilter() {
 }