Change ProcessThread's task type to be the one from TaskQueue.
ProcessThread will eventually be replaced by TaskQueue, so this is the first little step.

BUG=
R=magjed@webrtc.org

Review URL: https://codereview.webrtc.org/2016043003 .

Cr-Commit-Position: refs/heads/master@{#12952}
diff --git a/webrtc/modules/video_coding/jitter_buffer_unittest.cc b/webrtc/modules/video_coding/jitter_buffer_unittest.cc
index 9bdce7a..56e4116 100644
--- a/webrtc/modules/video_coding/jitter_buffer_unittest.cc
+++ b/webrtc/modules/video_coding/jitter_buffer_unittest.cc
@@ -195,7 +195,7 @@
   MOCK_METHOD1(WakeUp, void(Module* module));
   MOCK_METHOD1(RegisterModule, void(Module* module));
   MOCK_METHOD1(DeRegisterModule, void(Module* module));
-  void PostTask(std::unique_ptr<ProcessTask> task) {}
+  void PostTask(std::unique_ptr<rtc::QueuedTask> task) /*override*/ {}
 };
 
 class TestBasicJitterBuffer : public ::testing::TestWithParam<std::string>,