EDK: Add a mojo::test::SimpleTestThread (and use it).

mojo/edk/system/raw_channel_unittest.cc

Index: mojo/edk/system/raw_channel_unittest.cc
diff --git a/mojo/edk/system/raw_channel_unittest.cc b/mojo/edk/system/raw_channel_unittest.cc
index 0d6f2c3226705d9a0ea56ba9136ca909a2e48368..3921281a90b09d08964bdbfca498170ec6af7e07 100644
--- a/mojo/edk/system/raw_channel_unittest.cc
+++ b/mojo/edk/system/raw_channel_unittest.cc
@@ -16,7 +16,6 @@
 #include "base/logging.h"
 #include "base/memory/scoped_vector.h"
 #include "base/synchronization/waitable_event.h"
-#include "base/threading/simple_thread.h"
 #include "mojo/edk/embedder/platform_channel_pair.h"
 #include "mojo/edk/embedder/platform_handle.h"
 #include "mojo/edk/embedder/scoped_platform_handle.h"
@@ -25,6 +24,7 @@
 #include "mojo/edk/system/test_utils.h"
 #include "mojo/edk/system/transport_data.h"
 #include "mojo/edk/test/scoped_test_dir.h"
+#include "mojo/edk/test/simple_test_thread.h"
 #include "mojo/edk/test/test_io_thread.h"
 #include "mojo/edk/test/test_utils.h"
 #include "mojo/edk/util/make_unique.h"
@@ -308,12 +308,10 @@ TEST_F(RawChannelTest, OnReadMessage) {
 
 // RawChannelTest.WriteMessageAndOnReadMessage ---------------------------------
 
-class RawChannelWriterThread : public base::SimpleThread {
+class RawChannelWriterThread : public mojo::test::SimpleTestThread {
  public:
   RawChannelWriterThread(RawChannel* raw_channel, size_t write_count)
-      : base::SimpleThread("raw_channel_writer_thread"),
-        raw_channel_(raw_channel),
-        left_to_write_(write_count) {}
+      : raw_channel_(raw_channel), left_to_write_(write_count) {}
 
   ~RawChannelWriterThread() override { Join(); }