Fix missing 'break' in DocumentLifeCycle::CanAdvanceTo

No test is added because this is a DHCECK_IS_ON only method.

Bug: 808047
Change-Id: I615a07aec4223dd4c029f6e59dc864ffc7a0f739
Reviewed-on: https://chromium-review.googlesource.com/897053Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534154}

third_party/WebKit/Source/core/dom/DocumentLifecycle.cpp

@@ -222,7 +222,7 @@ bool DocumentLifecycle::CanAdvanceTo(LifecycleState next_state) const {
       // Otherwise, we can continue onwards.
       if (next_state == kCompositingClean)
         return true;
-      FALLTHROUGH;  // TODO(thakis): Intended? https://crbug.com/808047
+      break;
     case kCompositingClean:
       DCHECK(!RuntimeEnabledFeatures::SlimmingPaintV2Enabled());
       if (next_state == kInStyleRecalc)