Add undocumented Memory.* histograms to histograms.xml.

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 c839204da710e96ee004ae78689ab07daafaa56b..badf5a5f1696c68a40edef5617e3af84f72a2006 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -24228,7 +24228,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.ChromeProcessCount">
+<histogram name="Memory.ChromeProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
@@ -24273,6 +24273,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Memory.ExtensionProcessCount" units="processes">
+  <owner>hajimehoshi@chromium.org</owner>
+  <owner>kenjibaheux@google.com</owner>
+  <owner>kouhei@chromium.org</owner>
+  <summary>
+    The count of active extension processes.  Recorded once per UMA ping.
+  </summary>
+</histogram>
+
 <histogram name="Memory.GlyphPagesPerLoad">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
@@ -24418,7 +24427,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.OtherProcessCount">
+<histogram name="Memory.OtherProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
@@ -24456,7 +24465,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.PepperPluginBrokerProcessCount">
+<histogram name="Memory.PepperPluginBrokerProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
@@ -24466,7 +24475,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.PepperPluginProcessCount">
+<histogram name="Memory.PepperPluginProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
@@ -24488,7 +24497,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.PluginProcessCount">
+<histogram name="Memory.PluginProcessCount" units="processes">
   <obsolete>
     Deprecated due to NPAPI removal.
   </obsolete>
@@ -24517,7 +24526,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.ProcessCount">
+<histogram name="Memory.ProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
@@ -24579,7 +24588,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.RendererProcessCount">
+<histogram name="Memory.RendererProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
@@ -24987,6 +24996,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Memory.Swap.Zygote" units="KB">
+  <owner>hajimehoshi@chromium.org</owner>
+  <owner>kenjibaheux@google.com</owner>
+  <owner>kouhei@chromium.org</owner>
+  <summary>
+    The swap used by the zygote process.  Recorded once per UMA ping if the
+    system has swapped.
+  </summary>
+</histogram>
+
 <histogram name="Memory.Total" units="MB">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
@@ -25029,11 +25048,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Memory.WorkerProcessCount">
+<histogram name="Memory.WorkerProcessCount" units="processes">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
-  <summary>TBD.</summary>
+  <summary>
+    The count of active worker processes.  Recorded once per UMA ping.
+  </summary>
+</histogram>
+
+<histogram name="Memory.Zygote" units="KB">
+  <owner>hajimehoshi@chromium.org</owner>
+  <owner>kenjibaheux@google.com</owner>
+  <owner>kouhei@chromium.org</owner>
+  <summary>
+    The private working set used by the zygote process.  Each zygote process
+    provides one sample.  Recorded once per UMA ping.
+  </summary>
 </histogram>
 
 <histogram name="MemoryAndroid.DeviceMemoryClass">