experiment with -Wimplicit-fallthrough

base/third_party/dmg_fp/dtoa_wrapper.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // The purpose of this file is to supply the macro definintions necessary
 // to make third_party/dmg_fp/dtoa.cc threadsafe.
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/synchronization/lock.h"
 
@@ skipping 25 matching lines @@
   base::Lock* lock = n == 0 ? dtoa_lock_0.Pointer() : dtoa_lock_1.Pointer();
   lock->Acquire();
 }
 
 inline static void FREE_DTOA_LOCK(size_t n) {
   DCHECK(n < 2);
   base::Lock* lock = n == 0 ? dtoa_lock_0.Pointer() : dtoa_lock_1.Pointer();
   lock->Release();
 }
 
+
+// dtoa.cc intentionally uses fallthroughs.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wimplicit-fallthrough"
+
 #include "base/third_party/dmg_fp/dtoa.cc"
+
+#pragma clang diagnostic pop