JankTracker logging: add URL and exclude devtools.

This tweaks the DVLOG output of JankTracker to be more useful, printing
the URL of the document in which the layout shift occurred, indicating
whether it's in a subframe, and suppressing output for devtools windows.

Bug: 581518
Change-Id: I5515137219a6ff88fb46ca9181f500e5b23c191d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1459802Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659612}

third_party/blink/renderer/core/layout/jank_tracker.cc

@@ -96,6 +96,12 @@ static void RegionToTracedValue(const JankRegion& region,
   RegionToTracedValue(old_region, granularity_scale, value);
 }
 
+#if DCHECK_IS_ON()
+static bool ShouldLog(const LocalFrame& frame) {
+  return !frame.GetDocument()->Url().GetString().StartsWith("chrome-devtools:");
+}
+#endif
+
 JankTracker::JankTracker(LocalFrameView* frame_view)
     : frame_view_(frame_view),
       score_(0.0),
@@ -145,8 +151,15 @@ void JankTracker::AccumulateJank(const LayoutObject& source,
   if (!old_rect.Intersects(viewport) && !new_rect.Intersects(viewport))
     return;
 
-  DVLOG(2) << source.DebugName() << " moved from " << old_rect.ToString()
-           << " to " << new_rect.ToString();
+#if DCHECK_IS_ON()
+  LocalFrame& frame = frame_view_->GetFrame();
+  if (ShouldLog(frame)) {
+    DVLOG(2) << "in " << (frame.IsMainFrame() ? "" : "subframe ")
+             << frame.GetDocument()->Url().GetString() << ", "
+             << source.DebugName() << " moved from " << old_rect.ToString()
+             << " to " << new_rect.ToString();
+  }
+#endif
 
   max_distance_ =
       std::max(max_distance_, GetMoveDistance(old_rect, new_rect, source));
@@ -249,10 +262,15 @@ void JankTracker::NotifyPrePaintFinished() {
 
   score_ += jank_fraction;
 
-  DVLOG(1) << "viewport " << (jank_fraction * 100)
-           << "% janked, raising score to " << score_;
-
   LocalFrame& frame = frame_view_->GetFrame();
+#if DCHECK_IS_ON()
+  if (ShouldLog(frame)) {
+    DVLOG(1) << "in " << (frame.IsMainFrame() ? "" : "subframe ")
+             << frame.GetDocument()->Url().GetString() << ", viewport was "
+             << (jank_fraction * 100) << "% janked; raising score to "
+             << score_;
+  }
+#endif
 
   TRACE_EVENT_INSTANT2("loading", "FrameLayoutJank", TRACE_EVENT_SCOPE_THREAD,
                        "data",