Add sub-metrics for Event.Latency.TouchToFirstScrollUpdateSwapBegin

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 75f16fdd33e2dc9286685a4235553e439a553fba..d448c6f206a0ea8632b96cb26a459453bb5a9a37 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -13092,6 +13092,58 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="Event.Latency.FirstScrollUpdate.BrowserNotifiedToBeforeGpuSwap"
+    units="microseconds">
+  <owner>rbyers@chromium.org</owner>
+  <summary>
+    Time between the browser receives the notification of a ScrollUpdate gesture
+    event induced renderer swap and GPU starts to swap if that ScrollUpdate is
+    the first such in a given scroll gesture event sequence.
+  </summary>
+</histogram>
+
+<histogram name="Event.Latency.FirstScrollUpdate.GpuSwap" units="microseconds">
+  <owner>rbyers@chromium.org</owner>
+  <summary>
+    Time between gpu starts to swap a ScrollUpdate gesture event induced frame
+    and the swap finishes if that ScrollUpdate is the first such in a given
+    scroll gesture event sequence.
+  </summary>
+</histogram>
+
+<histogram name="Event.Latency.FirstScrollUpdate.HandledToRendererSwap"
+    units="microseconds">
+  <owner>rbyers@chromium.org</owner>
+  <summary>
+    Time between the ScrollUpdate gesture event is handled on main/impl thread
+    (specified by suffix) and before renderer starts to swap if that
+    ScrollUpdate is the first such in a given scroll gesture event sequence.
+  </summary>
+</histogram>
+
+<histogram name="Event.Latency.FirstScrollUpdate.RendererSwapToBrowserNotified"
+    units="microseconds">
+  <owner>rbyers@chromium.org</owner>
+  <summary>
+    Time between the renderer starts to swap a frame induced by ScrollUpdate
+    gesture event and browser receives the swap notification if that
+    ScrollUpdate is the first such in a given scroll gesture event sequence.
+  </summary>
+</histogram>
+
+<histogram name="Event.Latency.FirstScrollUpdate.TouchToHandled"
+    units="microseconds">
+  <owner>rbyers@chromium.org</owner>
+  <summary>
+    Time between initial creation of a touch event and the generated
+    ScrollUpdate gesture event is handled on main/impl thread (specified by
+    suffix) if that ScrollUpdate is the first such in a given scroll gesture
+    event sequence. If no swap was induced by the ScrollUpdate gesture event, no
+    recording is made.
+  </summary>
+</histogram>
+
 <histogram name="Event.Latency.HitTest" units="microseconds">
   <owner>dtapuska@chromium.org</owner>
   <summary>