Cleanup of iOS AudioDevice implementation

TBR=tkchin
BUG=webrtc:4789
TEST=modules_unittests --gtest_filter=AudioDeviceTest* and AppRTCDemo

Review URL: https://codereview.webrtc.org/1206783002 .

Cr-Commit-Position: refs/heads/master@{#9578}
diff --git a/webrtc/base/logging.cc b/webrtc/base/logging.cc
index 1ac1373..58f8f58 100644
--- a/webrtc/base/logging.cc
+++ b/webrtc/base/logging.cc
@@ -37,6 +37,7 @@
 #include <vector>
 
 #include "webrtc/base/logging.h"
+#include "webrtc/base/platform_thread.h"
 #include "webrtc/base/scoped_ptr.h"
 #include "webrtc/base/stringencode.h"
 #include "webrtc/base/stringutils.h"
@@ -111,10 +112,8 @@
   }
 
   if (thread_) {
-#if defined(WEBRTC_WIN)
-    DWORD id = GetCurrentThreadId();
-    print_stream_ << "[" << std::hex << id << std::dec << "] ";
-#endif  // WEBRTC_WIN
+    PlatformThreadId id = CurrentThreadId();
+    print_stream_ << "[" << std::dec << id << "] ";
   }
 
   if (err_ctx != ERRCTX_NONE) {