Create and pass shared-histogram-allocator from browser to renderer.

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 50a4aef8b5450adb0ff0b5674c9c971dc4593434..3d656990e635849060b597672ad2315cbc2abb2c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -54183,6 +54183,24 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.PersistentAllocator.RendererMetrics.Allocs" units="bytes">
+  <owner>bcwhite@chromium.org</owner>
+  <owner>asvitkine@chromium.org</owner>
+  <summary>
+    Size, before padding, of objects allocated from persistent memory. This is
+    updated with every allocation.
+  </summary>
+</histogram>
+
+<histogram name="UMA.PersistentAllocator.RendererMetrics.UsedPct" units="%">
+  <owner>bcwhite@chromium.org</owner>
+  <owner>asvitkine@chromium.org</owner>
+  <summary>
+    Percentage of persistent memory segment that has been allocated. This is
+    updated only once per reporting cycle.
+  </summary>
+</histogram>
+
 <histogram name="UMA.PersistentAllocator.SetupMetrics.Allocs" units="bytes">
   <owner>bcwhite@chromium.org</owner>
   <owner>asvitkine@chromium.org</owner>
@@ -54257,6 +54275,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.SubprocessMetricsProvider.SubprocessCount" units="count">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    The number of subprocesses from which persistent metrics were collected
+    during the last reporting cycle.
+  </summary>
+</histogram>
+
 <histogram name="UMA.SyntheticTrials.Count">
   <obsolete>
     Deprecated as of August 2015.