Add UMA for PurgeAndSuspend.

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 bb600012d13f87872d83ad8ec7daebcc3f7be012..020567e4398be9526e08fe9397814bab1ae0fa2a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -25407,6 +25407,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>The current process limit.  Recorded once per UMA ping.</summary>
 </histogram>
 
+<histogram name="Memory.PurgeAndSuspend">
+  <owner>tasak@google.com</owner>
+  <summary>
+    The memory usage after a background renderer is purged and suspended. Note:
+    this metric is for A/B testing.
+  </summary>
+</histogram>
+
 <histogram name="Memory.Renderer" units="KB">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
@@ -108411,6 +108419,20 @@ value.
   <affected-histogram name="PLT.BeginToFinish_NormalLoad"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="PurgeAndSuspend" separator=".">
+  <suffix name="BlinkGCKB" label="The memory usage of the BlinkGC allocator"/>
+  <suffix name="DiscardableKB"
+      label="The memory usage of the discardable memory"/>
+  <suffix name="MallocMB" label="The memory usage of the malloc"/>
+  <suffix name="PartitionAllocKB" label="The memory usage of PartitionAlloc"/>
+  <suffix name="TotalAllocatedMB"
+      label="The sum of the memory usages of PartitionAlloc, malloc,
+             discardable memory, mainThreadIsolate() and BlinkGC allocator"/>
+  <suffix name="V8MainThreadIsolateMB"
+      label="The memory usage of mainThreadIsolate()"/>
+  <affected-histogram name="Memory.PurgeAndSuspend"/>
+</histogram_suffixes>

[Ilya Sherman, 2016/10/13 00:43:03]

Since the histograms now use a mix of units, I don't think it's as appropriate
to use histogram_suffixes now.  It's better for each histogram to have the
appropriate units attribute listed in this file.

[tasak, 2016/10/13 03:56:16]

I see.
Thank you.
Done.

+
 <histogram_suffixes name="QueryTimeSuffix" separator=".">
   <suffix name="0" label="N = 0"/>
   <suffix name="1" label="N = 1"/>