Clang style plugin: add warn-only option and use it on Windows

tools/clang/plugins/tests/warn_only.cpp

Index: tools/clang/plugins/tests/warn_only.cpp
diff --git a/media/base/video_capturer_source.cc b/tools/clang/plugins/tests/warn_only.cpp
similarity index 55%
copy from media/base/video_capturer_source.cc
copy to tools/clang/plugins/tests/warn_only.cpp
index c1ebbe1dbff339455a2ef2e9b09efc95edfe79c1..1fbefcb105b911baaafd4b1753353f3e35d3e319 100644
--- a/media/base/video_capturer_source.cc
+++ b/tools/clang/plugins/tests/warn_only.cpp
@@ -2,10 +2,4 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "media/base/video_capturer_source.h"
-
-namespace media {
-
-VideoCapturerSource::~VideoCapturerSource() {}
-
-}  // namespace media
+#include "warn_only.h"