Add main thread scrolling reasons to GraphicsLayer::layerTreeAsJSON.

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
index 4b444f9b9237fa328f1dcbec4003f9b4d6c1f077..c93735f9e4985b25b10b7f9e9c0e8d67b8d11e2b 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -347,12 +347,14 @@ void ScrollingCoordinator::scrollableAreaScrollbarLayerDidChange(ScrollableArea*
         if (scrollbar.isCustomScrollbar()) {
             detachScrollbarLayer(scrollbarGraphicsLayer);
             scrollbarGraphicsLayer->platformLayer()->addMainThreadScrollingReasons(MainThreadScrollingReason::kCustomScrollbarScrolling);
+            scrollbarGraphicsLayer->debugInfo().setMainThreadScrollingReasons(scrollbarGraphicsLayer->platformLayer()->mainThreadScrollingReasons());
             return;
         }
 
         // Invalidate custom scrollbar scrolling reason in case a custom
         // scrollbar becomes a non-custom one.
         scrollbarGraphicsLayer->platformLayer()->clearMainThreadScrollingReasons(MainThreadScrollingReason::kCustomScrollbarScrolling);
+        scrollbarGraphicsLayer->debugInfo().setMainThreadScrollingReasons(scrollbarGraphicsLayer->platformLayer()->mainThreadScrollingReasons());
         WebScrollbarLayer* scrollbarLayer = getWebScrollbarLayer(scrollableArea, orientation);
         if (!scrollbarLayer) {
             Settings* settings = m_page->mainFrame()->settings();
@@ -680,12 +682,14 @@ void ScrollingCoordinator::setShouldUpdateScrollLayerPositionOnMainThread(MainTh
                 scrollAnimator->takeOverCompositorAnimation();
             }
             scrollLayer->addMainThreadScrollingReasons(mainThreadScrollingReasons);
+            layer->debugInfo().setMainThreadScrollingReasons(scrollLayer->mainThreadScrollingReasons());
         } else {
             // Clear all main thread scrolling reasons except the one that's set
             // if there is a running scroll animation.
             uint32_t mainThreadScrollingReasonsToClear = ~0u;
             mainThreadScrollingReasonsToClear &= ~MainThreadScrollingReason::kAnimatingScrollOnMainThread;
             scrollLayer->clearMainThreadScrollingReasons(mainThreadScrollingReasonsToClear);
+            layer->debugInfo().setMainThreadScrollingReasons(scrollLayer->mainThreadScrollingReasons());
         }
     }
 }
@@ -1043,33 +1047,16 @@ MainThreadScrollingReasons ScrollingCoordinator::mainThreadScrollingReasons() co
     return reasons;
 }
 
-String ScrollingCoordinator::mainThreadScrollingReasonsAsText(MainThreadScrollingReasons reasons)
-{
-    StringBuilder stringBuilder;
-
-    if (reasons & MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects)
-        stringBuilder.append("Has background-attachment:fixed, ");
-    if (reasons & MainThreadScrollingReason::kHasNonLayerViewportConstrainedObjects)
-        stringBuilder.append("Has non-layer viewport-constrained objects, ");
-    if (reasons & MainThreadScrollingReason::kHasStickyPositionObjects)
-        stringBuilder.append("Has sticky position objects, ");
-    if (reasons & MainThreadScrollingReason::kThreadedScrollingDisabled)
-        stringBuilder.append("Threaded scrolling is disabled, ");
-    if (reasons & MainThreadScrollingReason::kAnimatingScrollOnMainThread)
-        stringBuilder.append("Animating scroll on main thread, ");
-
-    if (stringBuilder.length())
-        stringBuilder.resize(stringBuilder.length() - 2);
-    return stringBuilder.toString();
-}
-
 String ScrollingCoordinator::mainThreadScrollingReasonsAsText() const
 {
     ASSERT(m_page->deprecatedLocalMainFrame()->document()->lifecycle().state() >= DocumentLifecycle::CompositingClean);
-    if (WebLayer* scrollLayer = toWebLayer(m_page->deprecatedLocalMainFrame()->view()->layerForScrolling()))
-        return mainThreadScrollingReasonsAsText(scrollLayer->mainThreadScrollingReasons());
+    if (WebLayer* scrollLayer = toWebLayer(m_page->deprecatedLocalMainFrame()->view()->layerForScrolling())) {
+        String result(MainThreadScrollingReason::mainThreadScrollingReasonsAsText(scrollLayer->mainThreadScrollingReasons()).c_str());
+        return result;
+    }
 
-    return mainThreadScrollingReasonsAsText(m_lastMainThreadScrollingReasons);
+    String result(MainThreadScrollingReason::mainThreadScrollingReasonsAsText(m_lastMainThreadScrollingReasons).c_str());
+    return result;
 }
 
 bool ScrollingCoordinator::frameViewIsDirty() const