Adding cache hit/miss histograms to DiskBasedCertCache.

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 e35ae92e0c9f08a2a52273a11e3c56362403f57b..bafb05aa560f4360c6471bea5226ba1341c2d0e6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3499,6 +3499,22 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="DiskBasedCertCache.DiskCacheHit" enum="CacheHit">
+  <owner>brandonsalmon@chromium.org</owner>
+  <summary>
+    Whether or not a certificate was found cached on disk by the
+    DiskBasedCertCache.
+  </summary>
+</histogram>
+
+<histogram name="DiskBasedCertCache.MemCacheHit" enum="CacheHit">
+  <owner>brandonsalmon@chromium.org</owner>
+  <summary>
+    Whether or not a certificate was found in DiskBasedCertCache's in-memory MRU
+    cache.
+  </summary>
+</histogram>
+
 <histogram name="DiskCache.0.FilesAge" units="hours">
   <owner>rvargas@chromium.org</owner>
   <summary>The age of the cache's files (wall time).</summary>
@@ -35319,6 +35335,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="3" label="HTTP_STREAM_FACTORY_IMPL_JOB_MAIN"/>
 </enum>
 
+<enum name="CacheHit" type="int">

[Ryan Sleevi, 2014/07/09 19:00:52]

Jar can confirm, but I believe the preference is to name these Boolean-prefix
style

(BooleanHit?)

More of a nit though.

+  <int value="0" label="Miss"/>
+  <int value="1" label="Hit"/>
+</enum>
+
 <enum name="CanvasContextType" type="int">
   <int value="0" label="2d"/>
   <int value="1" label="webkit-3d"/>