Fix broken MainThreadScrollingReason DCHECK.

cc/input/main_thread_scrolling_reason.h

Index: cc/input/main_thread_scrolling_reason.h
diff --git a/cc/input/main_thread_scrolling_reason.h b/cc/input/main_thread_scrolling_reason.h
index 4de70f7ef779fa28794cb492bf21af22a38803ad..50514e677b71f278c872a6393273e606b05dd825 100644
--- a/cc/input/main_thread_scrolling_reason.h
+++ b/cc/input/main_thread_scrolling_reason.h
@@ -16,7 +16,9 @@ struct MainThreadScrollingReason {
   enum : uint32_t { kThreadedScrollingDisabled = 1 << 2 };
   enum : uint32_t { kScrollbarScrolling = 1 << 3 };
   enum : uint32_t { kPageOverlay = 1 << 4 };
-  enum : uint32_t { kMaxNonTransientScrollingReason = kPageOverlay };
+  // The maximum value reachable as a combination of the non-transient scrolling
+  // reasons.
+  enum : uint32_t { kMaxNonTransientScrollingReasons = (1 << 5) - 1 };
 
   // Transient scrolling reasons. These are computed for each scroll begin.
   enum : uint32_t { kNonFastScrollableRegion = 1 << 5 };