Add separate trace events for recalcStyle and rebuildLayoutTree.

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

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 218fbb4fc990ab0f36a65a55e3ae4411379dc5da..427579c1582651136ce92112064610bc0d7b5ff4 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -2100,11 +2100,15 @@ void Document::updateStyle() {
 
   if (Element* documentElement = this->documentElement()) {
     inheritHtmlAndBodyElementStyles(change);
-    if (documentElement->shouldCallRecalcStyle(change))
+    if (documentElement->shouldCallRecalcStyle(change)) {
+      TRACE_EVENT0("blink,blink_style", "Document::recalcStyle");
       documentElement->recalcStyle(change);
+    }
     if (documentElement->needsReattachLayoutTree() ||
-        documentElement->childNeedsReattachLayoutTree())
+        documentElement->childNeedsReattachLayoutTree()) {
+      TRACE_EVENT0("blink,blink_style", "Document::rebuildLayoutTree");
       documentElement->rebuildLayoutTree();
+    }
   }
 
   view()->recalcOverflowAfterStyleChange();