Renderer.LineLayoutMs UMA histogram to measure line layout time.

Source/core/rendering/RenderBlockLineLayout.cpp

Index: Source/core/rendering/RenderBlockLineLayout.cpp
diff --git a/Source/core/rendering/RenderBlockLineLayout.cpp b/Source/core/rendering/RenderBlockLineLayout.cpp
index 5a242d576aaf609ede35354df22665b0175ed864..2ce9a4cfe032f95eb395cde6315cbc2cb6a7e6eb 100644
--- a/Source/core/rendering/RenderBlockLineLayout.cpp
+++ b/Source/core/rendering/RenderBlockLineLayout.cpp
@@ -767,7 +767,9 @@ void RenderBlockFlow::layoutRunsAndFloats(LineLayoutState& layoutState)
         }
     }
 
+    double start = WTF::currentTimeMS();
     layoutRunsAndFloatsInRange(layoutState, resolver, cleanLineStart, cleanLineBidiStatus);
+    frameView()->lineLayoutTime(WTF::currentTimeMS() - start);
     linkToEndLineIfNeeded(layoutState);
     markDirtyFloatsForPaintInvalidation(layoutState.floats());
 }