Ad metrics: Fix memory metric ranges and units.

This change fixes the ranges for
PageLoad.Clients.Ads.Memory.MainFrame.Max and
PageLoad.Clients.Ads.Memory.UpdateCount, which were initially too
small.

This CL also replaces 'bytes' with 'kilobytes' in the histogram
descriptions of the PageLoad.Clients.Ads.Memory.*.Max metrics.

We are not versioning the metrics as this is a bug fix just a couple
days after launch.

Bug: 1136598
Change-Id: I790abcf40d0469469ad519401470bcd09ced59ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462339Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: John Delaney <johnidel@chromium.org>
Commit-Queue: Cammie Smith Barnes <cammie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816780}

chrome/browser/page_load_metrics/observers/ad_metrics/ads_page_load_metrics_observer.cc

@@ -1049,10 +1049,10 @@ void AdsPageLoadMetricsObserver::RecordAggregateHistogramsForAdTagging(
   ADS_HISTOGRAM("Bytes.MainFrame.Ads.Total2", PAGE_BYTES_HISTOGRAM, visibility,
                 main_frame_data_->ad_bytes());
   if (memory_request_) {
-    UMA_HISTOGRAM_COUNTS_1000("PageLoad.Clients.Ads.Memory.MainFrame.Max",
-                              main_frame_data_->v8_max_memory_bytes_used());
-    UMA_HISTOGRAM_COUNTS_1000("PageLoad.Clients.Ads.Memory.UpdateCount",
-                              num_memory_updates_);
+    PAGE_BYTES_HISTOGRAM("PageLoad.Clients.Ads.Memory.MainFrame.Max",
+                         main_frame_data_->v8_max_memory_bytes_used());
+    UMA_HISTOGRAM_COUNTS_10000("PageLoad.Clients.Ads.Memory.UpdateCount",
+                               num_memory_updates_);
     UMA_HISTOGRAM_COUNTS_1000(
         "PageLoad.Clients.Ads.Memory.MissedMeasurementCount",
         num_missed_memory_measurements_);

tools/metrics/histograms/histograms_xml/page/histograms.xml

@@ -232,8 +232,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>jkarlin@chromium.org</owner>
   <owner>johnidel@chromium.org</owner>
   <summary>
-    The maximum reported number of bytes of memory used by V8 by the main frame
-    in this pageload.
+    The maximum reported number of kilobytes of memory used by V8 by the main
+    frame in this pageload.
 
     Only recorded if the page has at least one identified ad frame. Recorded in
     PageLoadMetrics when the page is destroyed. An ad frame consists of the
@@ -1805,8 +1805,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>jkarlin@chromium.org</owner>
   <owner>johnidel@chromium.org</owner>
   <summary>
-    The maximum reported aggregate number of bytes of memory used by V8 by ad
-    frames in this pageload. The value recorded is the maximum simultaneous
+    The maximum reported aggregate number of kilobytes of memory used by V8 by
+    ad frames in this pageload. The value recorded is the maximum simultaneous
     usage by ad frames during this pageload.
 
     Only recorded if the page has at least one identified ad frame. Recorded in
@@ -1822,8 +1822,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>jkarlin@chromium.org</owner>
   <owner>johnidel@chromium.org</owner>
   <summary>
-    The maximum reported number of bytes of memory used by V8 by frames in the
-    ad frame tree in this pageload. The value recorded is the maximum
+    The maximum reported number of kilobytes of memory used by V8 by frames in
+    the ad frame tree in this pageload. The value recorded is the maximum
     simultaneous usage by ad frames in this ad frame tree.
 
     Only recorded if the page has at least one identified ad frame. Recorded in