Experimental CompressibleString UMA

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 a5730980efea7fd0734213de59c42119a4fce2f9..e0a27b5af112b9883f2930b7843bc04a6c49137e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19839,6 +19839,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Memory.CompressibleStringCount"
+    enum="CompressibleStringCountType">
+  <owner>hajimehoshi@chromium.org</owner>
+  <summary>
+    The count of CompressibleString for JavaScript source stirngs in a
+    background tab. This checks how often V8 requires JavaScript source strings
+    and decopressing is required in the background tab.
+  </summary>
+</histogram>
+
 <histogram name="Memory.DiscardableAllocationSize" units="KB">
   <owner>reveman@chromium.org</owner>
   <summary>
@@ -58512,6 +58522,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1" label="GPU compositor"/>
 </enum>
 
+<enum name="CompressibleStringCountType" type="int">
+  <int value="0" label="Compressed in a background tab"/>
+  <int value="1" label="Decompressed in a background tab"/>
+</enum>
+
 <enum name="ComputeCurrentSigninStatus" type="int">
   <int value="0" label="Tried to compute current signin status."/>
   <int value="1" label="Error: No profiles found."/>