Bug 1447480 - Add a MOZ_ASSERT to make it clear that it can never fall through r=hsivonen

MozReview-Commit-ID: Hq9jG1CVwRK

--HG--
extra : rebase_source : 4c548c1ad0c74b2c810b435701b91bd4f7893cb1

parser/html/javasrc/TreeBuilder.java

@@ -1167,6 +1167,7 @@ public abstract class TreeBuilder<T> implements TokenHandler,
                                      */
                                     continue;
                             }
+                            // CPPONLY: MOZ_FALLTHROUGH_ASSERT();
                         default:
                             /*
                              * A character token that is not one of one of

parser/html/nsHtml5TreeBuilder.cpp

@@ -399,6 +399,7 @@ nsHtml5TreeBuilder::characters(const char16_t* buf,
                 continue;
               }
             }
+            MOZ_FALLTHROUGH_ASSERT();
           }
           default: {
             switch (mode) {