ServiceWorker: Add UMA for ServiceWorkerDiskCache

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 8f7b359fc5b5ac29e47cf758b38e7a20d9839daa..ecbeeb80a85db8a0fcc46674a9ee088dcbc2cef5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -24539,6 +24539,29 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="ServiceWorker.DiskCache.InitResult">
+  <owner>nhiroki@chromium.org</owner>
+  <summary>
+    Records result of opening a disk cache for ServiceWorkerDiskCache.
+  </summary>
+</histogram>
+
+<histogram name="ServiceWorker.DiskCache.ReadResponseResult"
+    enum="ServiceWorkerReadResponseResult">
+  <owner>nhiroki@chromium.org</owner>
+  <summary>
+    Records result of reading response from ServiceWorkerDiskCache.
+  </summary>
+</histogram>
+
+<histogram name="ServiceWorker.DiskCache.WriteResponseResult"
+    enum="ServiceWorkerWriteResponseResult">
+  <owner>nhiroki@chromium.org</owner>
+  <summary>
+    Records result of writing response into ServiceWorkerDiskCache.
+  </summary>
+</histogram>
+
 <histogram name="Settings.DefaultSearchProvider" enum="OmniboxSearchEngine">
   <obsolete>
     Deprecated in Chrome 30.  Use Search.DefaultSearchProviderType instead.
@@ -42813,6 +42836,18 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="4" label="Operation Error"/>
 </enum>
 
+<enum name="ServiceWorkerReadResponseResult" type="int">
+  <int value="0" label="OK"/>
+  <int value="1" label="Read headers error"/>
+  <int value="2" label="Read data error"/>
+</enum>
+
+<enum name="ServiceWorkerWriteResponseResult" type="int">
+  <int value="0" label="OK"/>
+  <int value="1" label="Write headers error"/>
+  <int value="2" label="Write data error"/>
+</enum>
+
 <enum name="SessionStartupPref" type="int">
   <int value="0" label="Open home page (unused)"/>
   <int value="1" label="Continue from last opened pages"/>