[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 543fa7e2cc5986675dd7fe8705bbb80713bfbfd2..6ba54decf59909fbc819e1b9f3e3f2cae9c682a8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -42416,12 +42416,36 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Experimental.Bytes.Cache.OnComplete" 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.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Experimental.Bytes.Network.OnComplete" 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.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Experimental.Bytes.Total.OnComplete" 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.
+  </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>
 
@@ -42429,7 +42453,7 @@ 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>
@@ -42526,7 +42550,7 @@ 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>