Remaining changes to build all code in src.git with -Wimplicit-fallthrough.

This CL was uploaded by git cl split.

R=sdefresne@chromium.org

Bug: 177475
Change-Id: Iae7090f66ed567d16e3c3174949a4399b3ca6ad9
Reviewed-on: https://chromium-review.googlesource.com/891879Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532864}

components/history/core/browser/history_backend.cc

@@ -648,7 +648,8 @@ void HistoryBackend::InitImpl(
       // The frequency of this UMA will indicate how often history
       // initialization fails.
       UMA_HISTOGRAM_BOOLEAN("History.AttemptedToFixProfileError", kill_db);
-    }  // Falls through.
+      FALLTHROUGH;
+    }
     case sql::INIT_TOO_NEW: {
       db_diagnostics_ += sql::GetCorruptFileDiagnosticsInfo(history_name);
       delegate_->NotifyProfileError(status, db_diagnostics_);

components/history/core/browser/history_backend_unittest.cc

@@ -1373,6 +1373,7 @@ TEST_F(HistoryBackendTest, AddPageVisitSource) {
         break;
       case history::SOURCE_SYNCED:
         sources |= 0x4;
+        break;
       default:
         break;
     }