Use per-frame task runners instead of per-thread task runners at pepper module

This CL is based on Alexander's CL: https://chromium-review.googlesource.com/c/chromium/src/+/1367329

Bug: 870606
Change-Id: I2ca696efeb203d7cb48c9f33034163c2d9c6277d
Reviewed-on: https://chromium-review.googlesource.com/c/1379607
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Alexander Timin <[email protected]>
Reviewed-by: Bill Budge <[email protected]>
Commit-Queue: Hajime Hoshi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#620986}
diff --git a/ppapi/proxy/plugin_dispatcher.cc b/ppapi/proxy/plugin_dispatcher.cc
index 67c9c3b..cdac7403 100644
--- a/ppapi/proxy/plugin_dispatcher.cc
+++ b/ppapi/proxy/plugin_dispatcher.cc
@@ -217,7 +217,8 @@
     const IPC::ChannelHandle& channel_handle,
     bool is_client) {
   if (!Dispatcher::InitWithChannel(delegate, peer_pid, channel_handle,
-                                   is_client))
+                                   is_client,
+                                   base::ThreadTaskRunnerHandle::Get()))
     return false;
   plugin_delegate_ = delegate;
   plugin_dispatcher_id_ = plugin_delegate_->Register(this);