Work on getting things built with -Wimplicit-fallthrough. This CL was uploaded by git cl split.

Bug: 177475
R=dtrainor@chromium.org

Change-Id: Iae75d4ee55a8246d599dff7b8519bc5115b40c9c
Reviewed-on: https://chromium-review.googlesource.com/889785Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532137}

content/browser/download/download_item_impl.cc

@@ -1891,6 +1891,7 @@ void DownloadItemImpl::InterruptWithPartialState(
       }
       // else - Fallthrough for cancellation handling which is equivalent to the
       // IN_PROGRESS state.
+      FALLTHROUGH;
 
     case IN_PROGRESS_INTERNAL:
     case TARGET_RESOLVED_INTERNAL: