Fix broken MainThreadScrollingReason DCHECK.

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1640373002

Cr-Commit-Position: refs/heads/master@{#371843}

cc/blink/web_layer_impl.cc

@@ -344,7 +344,7 @@ void WebLayerImpl::addMainThreadScrollingReasons(
   // TODO(tdresser): This is comparing less than a bit flag but that's not valid
   // if there is more than one reason given in |main_thread_scrolling_reasons|.
   DCHECK_LE(main_thread_scrolling_reasons,
-            cc::MainThreadScrollingReason::kMaxNonTransientScrollingReason);
+            cc::MainThreadScrollingReason::kMaxNonTransientScrollingReasons);
   layer_->AddMainThreadScrollingReasons(main_thread_scrolling_reasons);
 }
 

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 };

cc/trees/layer_tree_host_impl.cc

@@ -2500,10 +2500,10 @@ LayerImpl* LayerTreeHostImpl::FindScrollLayerForDeviceViewportPoint(
     if (status.thread == SCROLL_ON_MAIN_THREAD) {
       if (layer_impl->should_scroll_on_main_thread()) {
         DCHECK_LE(status.main_thread_scrolling_reasons,
-                  MainThreadScrollingReason::kMaxNonTransientScrollingReason);
+                  MainThreadScrollingReason::kMaxNonTransientScrollingReasons);
       } else {
         DCHECK_GT(status.main_thread_scrolling_reasons,
-                  MainThreadScrollingReason::kMaxNonTransientScrollingReason);
+                  MainThreadScrollingReason::kMaxNonTransientScrollingReasons);
       }
 
       *scroll_on_main_thread = true;
@@ -2522,10 +2522,10 @@ LayerImpl* LayerTreeHostImpl::FindScrollLayerForDeviceViewportPoint(
     if (status.thread == SCROLL_ON_MAIN_THREAD) {
       if (layer_impl->should_scroll_on_main_thread()) {
         DCHECK_LE(status.main_thread_scrolling_reasons,
-                  MainThreadScrollingReason::kMaxNonTransientScrollingReason);
+                  MainThreadScrollingReason::kMaxNonTransientScrollingReasons);
       } else {
         DCHECK_GT(status.main_thread_scrolling_reasons,
-                  MainThreadScrollingReason::kMaxNonTransientScrollingReason);
+                  MainThreadScrollingReason::kMaxNonTransientScrollingReasons);
       }
 
       *scroll_on_main_thread = true;