[PageLoadMetrics] Record bytes usage per page

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 f4daa9fa285d9c0d3878586eda425481634f4366..bfabea4f159f7878e7d44a9c4c6f01d83443c727 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -42813,12 +42813,37 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Experimental.Bytes.Cache" units="KB">
+  <owner>jkarlin@chromium.org</owner>
+  <summary>
+    The number of prefiltered (e.g., compressed) KiloBytes loaded from the cache
+    via the browser process for a page load. Recorded when the page is closed.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Experimental.Bytes.Network" units="KB">
+  <owner>jkarlin@chromium.org</owner>
+  <summary>
+    The number of prefiltered (e.g., compressed) KiloBytes loaded over the
+    network via the browser process for a page load. Recorded when the page is
+    closed.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Experimental.Bytes.Total" units="KB">
+  <owner>jkarlin@chromium.org</owner>
+  <summary>
+    The number of prefiltered (e.g., compressed) KiloBytes loaded via the
+    browser process for a page load. Recorded when the page is closed.
+  </summary>
+</histogram>
+
 <histogram name="PageLoad.Experimental.Cache.RequestPercent.ParseStop"
     units="%">
   <owner>csharrison@chromium.org</owner>
   <summary>
-    The percent of subresources loaded from cache for the given page load.
-    Recorded at the end of HTML parsing.
+    The percent of resources loaded from cache for the given page load. Recorded
+    at the end of HTML parsing.
   </summary>
 </histogram>
 
@@ -42826,7 +42851,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     units="requests">
   <owner>csharrison@chromium.org</owner>
   <summary>
-    The number of subresources a given page finished loading from cache at parse
+    The number of resources a given page finished loading from cache at parse
     stop.
   </summary>
 </histogram>
@@ -42923,7 +42948,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     units="requests">
   <owner>csharrison@chromium.org</owner>
   <summary>
-    The number of subresources a given page finished loading at parse stop.
+    The number of resources a given page finished loading at parse stop.
   </summary>
 </histogram>