experiment with -Wimplicit-fallthrough

base/third_party/icu/icu_utf.cc

Index: base/third_party/icu/icu_utf.cc
diff --git a/base/third_party/icu/icu_utf.cc b/base/third_party/icu/icu_utf.cc
index b47c8ac3c112307e22bedd677439618766f8e789..f943d0b7caba3aa1ee47ce9f452d6ab9daaab7f6 100644
--- a/base/third_party/icu/icu_utf.cc
+++ b/base/third_party/icu/icu_utf.cc
@@ -17,6 +17,7 @@
 *   that would otherwise be too long as macros.
 */
 
+#include "base/compiler_specific.h"
 #include "base/third_party/icu/icu_utf.h"
 
 namespace base_icu {
@@ -159,10 +160,12 @@ utf8_nextCharSafeBody(const uint8 *s, int32 *pi, int32 length, UChar32 c, UBool
                 illegal=1;
                 break;
             }
+            FALLTHROUGH_INTENDED;
         case 2:
             trail=s[(i)++];
             (c)=((c)<<6)|(trail&0x3f);
             illegal|=(trail&0xc0)^0x80;
+            FALLTHROUGH_INTENDED;
         case 1:
             trail=s[(i)++];
             (c)=((c)<<6)|(trail&0x3f);