Updates to support -Wimplicit-fallthrough

https://chromium-review.googlesource.com/c/chromium/mini_chromium/+/899847
turns the warning on. This adds one annotation, and fixes one bug.

Includes mini_chromium roll:

.../mini_chromium$ git log 5fcfa43c1587b94132e24782579350cb8266b990..3b953302848580cdf23b50402befc0ae09d03ff9 --oneline
3b95330 (HEAD, origin/master, origin/HEAD) Add -Wimplicit-fallthrough when building on clang

Bug: chromium:807632
Change-Id: I2f3ddca0228e52013844cb8d78d10cb359e851d0
Reviewed-on: https://chromium-review.googlesource.com/900317
Commit-Queue: Scott Graham <scottmg@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>

DEPS

@@ -28,7 +28,7 @@ deps = {
       '5e2b3ddde7cda5eb6bc09a5546a76b00e49d888f',
   'crashpad/third_party/mini_chromium/mini_chromium':
       Var('chromium_git') + '/chromium/mini_chromium@' +
-      '5fcfa43c1587b94132e24782579350cb8266b990',
+      '3b953302848580cdf23b50402befc0ae09d03ff9',
   'crashpad/third_party/zlib/zlib':
       Var('chromium_git') + '/chromium/src/third_party/zlib@' +
       '13dc246a58e4b72104d35f9b1809af95221ebda7',

handler/linux/exception_handler_server.cc

@@ -24,6 +24,7 @@
 
 #include <utility>
 
+#include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/string_number_conversions.h"
@@ -150,7 +151,7 @@ class PtraceStrategyDeciderImpl : public PtraceStrategyDecider {
         if (HaveCapSysPtrace()) {
           return Strategy::kDirectPtrace;
         }
-      // fallthrough
+        FALLTHROUGH;
       case PtraceScope::kNoAttach:
         LOG(WARNING) << "no ptrace";
         return Strategy::kNoPtrace;

minidump/minidump_context_writer.cc

@@ -84,6 +84,7 @@ MinidumpContextWriter::CreateFromSnapshot(const CPUContext* context_snapshot) {
       context = std::make_unique<MinidumpContextARM64Writer>();
       reinterpret_cast<MinidumpContextARM64Writer*>(context.get())
           ->InitializeFromSnapshot(context_snapshot->arm64);
+      break;
     }
 
     default: {