Enable -Wimplicit-fallthrough for linux debug too.

Bug: 177475
Change-Id: I7985f9356fcac3c4c2e05fc3cdda0b52d132c7c7
Reviewed-on: https://chromium-review.googlesource.com/896718
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533817}

build/config/compiler/BUILD.gn

@@ -1427,7 +1427,7 @@ config("chromium_code") {
   # Warn on missing break statements at the end of switch cases.
   # For intentional fallthrough, use FALLTHROUGH; from base/compiler_specific.h
   # TODO(thakis): Enable for all platforms, https://crbug.com/177475
-  if (is_clang && is_linux && !is_debug && !is_chromecast && !use_ozone) {
+  if (is_clang && is_linux && !is_chromecast && !use_ozone) {
     cflags += [ "-Wimplicit-fallthrough" ]
   }
 

net/disk_cache/blockfile/rankings.cc

@@ -83,10 +83,15 @@ enum CrashLocation {
 };
 
 #ifndef NDEBUG
-void TerminateSelf() {
+[[noreturn]] void TerminateSelf() {
 #if defined(OS_WIN)
   // Windows does more work on _exit() than we would like, so we force exit.
   TerminateProcess(GetCurrentProcess(), 0);
+#if defined(__clang__)
+  // Let clang know that TerminateProcess(GetCurrentProcess()) can't return,
+  // so that it doesn't warn about TerminateSelf() returning.
+  __builtin_unreachable();
+#endif
 #elif defined(OS_POSIX)
   // On POSIX, _exit() will terminate the process with minimal cleanup,
   // and it is cleaner than killing.

third_party/WebKit/Source/core/html/parser/AtomicHTMLToken.cpp

@@ -45,7 +45,7 @@ void AtomicHTMLToken::Show() const {
     case HTMLToken::kEndTag:
       if (self_closing_)
         printf(" selfclosing");
-    /* FALL THROUGH */
+      FALLTHROUGH;
     case HTMLToken::DOCTYPE:
       printf(" name \"%s\"", name_.GetString().Utf8().data());
       break;