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 6ed8bca0bace50c8eb32faea0692ecbe46404a6f..8068b3855971261623178a57aebc1bbab1e7e430 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -54913,6 +54913,24 @@ 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>
@@ -54987,6 +55005,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.SubprocessMetricsProvider.SubprocessCount"
+    units="subprocesses">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    The number of subprocesses from which persistent metrics were collected,
+    logged once with every reporting cycle.
+  </summary>
+</histogram>
+
 <histogram name="UMA.SyntheticTrials.Count">
   <obsolete>
     Deprecated as of August 2015.