Simple Cache: Add two optional stream 2 histograms

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 88c2894de57bb4ca1e38b0865527abc39e02b630..f979748aa848445a62eee3db95b227d960dd2037 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -14755,6 +14755,14 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="SimpleCache.App.EntryCreatedAndStream2Omitted"
+    enum="SimpleCache.EntryCreatedAndStream2Omitted">
+  <summary>
+    Whether, upon creation of a new cache entry, the file for stream 2 was
+    omitted since that stream was empty.
+  </summary>
+</histogram>
+
 <histogram name="SimpleCache.App.EntryCreationResult" enum="BooleanSuccess">
   <summary>
     For entry creation operations that were sent to the disk, the result of
@@ -14766,6 +14774,14 @@ other types of suffix sets.
   <summary>The time, in ms, spent creating a new entry on disk.</summary>
 </histogram>
 
+<histogram name="SimpleCache.App.EntryOpenedAndStream2Removed"
+    enum="SimpleCache.EntryOpenedAndStream2Removed">
+  <summary>
+    Whether, upon opening of an existing cache entry, stream 2 was empty and the
+    file for that stream was therefore removed.
+  </summary>
+</histogram>
+
 <histogram name="SimpleCache.App.EntryOperationsPending">
   <summary>
     At the time that operations are run, the number of pending operations on a
@@ -15454,6 +15470,14 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="SimpleCache.Http.EntryCreatedAndStream2Omitted"
+    enum="SimpleCache.EntryCreatedAndStream2Omitted">
+  <summary>
+    Whether, upon creation of a new cache entry, the file for stream 2 was
+    omitted since that stream was empty.
+  </summary>
+</histogram>
+
 <histogram name="SimpleCache.Http.EntryCreationResult" enum="BooleanSuccess">
   <summary>
     For entry creation operations that were sent to the disk, the result of
@@ -15465,6 +15489,14 @@ other types of suffix sets.
   <summary>The time, in ms, spent creating a new entry on disk.</summary>
 </histogram>
 
+<histogram name="SimpleCache.Http.EntryOpenedAndStream2Removed"
+    enum="SimpleCache.EntryOpenedAndStream2Removed">
+  <summary>
+    Whether, upon opening of an existing cache entry, stream 2 was empty and the
+    file for that stream was therefore removed.
+  </summary>
+</histogram>
+
 <histogram name="SimpleCache.Http.EntryOperationsPending">
   <summary>
     At the time that operations are run, the number of pending operations on a
@@ -25022,6 +25054,16 @@ other types of suffix sets.
   <int value="2" label="Dismiss"/>
 </enum>
 
+<enum name="SimpleCache.EntryCreatedAndStream2Omitted" type="int">
+  <int value="0" label="Stream 2 file was present"/>
+  <int value="1" label="Empty stream 2 file was omitted"/>
+</enum>
+
+<enum name="SimpleCache.EntryOpenedAndStream2Removed" type="int">
+  <int value="0" label="Stream 2 file was already omitted or not empty"/>
+  <int value="1" label="Empty stream 2 file removed"/>
+</enum>
+
 <enum name="SimpleCache.FileDescriptorLimitStatus" type="int">
   <int value="0" label="Unsupported"/>
   <int value="1" label="Supported but failed"/>