Add a use counter and histogram to FileReaderSync.

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 6e385b8b35952871d6b0c5f9db5570d5cb5f1b11..20b641c528180677148d26fe3921467871e7f32d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19444,6 +19444,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="FileReaderSync.WorkerType" enum="FileReaderSyncWorkerType">
+  <owner>mek@chromium.org</owner>
+  <summary>
+    For each FileReaderSync instance records the type of the web worker that
+    created the instance.
+  </summary>
+</histogram>
+
 <histogram name="FileSystem.DirectoryDatabaseInit"
     enum="FileSystemDatabaseInitResult">
   <owner>tzik@chromium.org</owner>
@@ -91134,6 +91142,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1809" label="V8DeprecatedStorageInfo_RequestQuota_Method"/>
   <int value="1810" label="V8DeprecatedStorageQuota_QueryUsageAndQuota_Method"/>
   <int value="1811" label="V8DeprecatedStorageQuota_RequestQuota_Method"/>
+  <int value="1812" label="V8FileReaderSync_Constructor"/>
 </enum>
 
 <enum name="FetchRequestMode" type="int">
@@ -91973,6 +91982,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="6" label="File could not be exclusively opened."/>
 </enum>
 
+<enum name="FileReaderSyncWorkerType" type="int">
+  <int value="0" label="Other"/>
+  <int value="1" label="Dedicated Worker"/>
+  <int value="2" label="Shared Worker"/>
+  <int value="3" label="Service Worker"/>
+</enum>
+
 <enum name="FileSystemDatabaseInitResult" type="int">
   <int value="0" label="OK"/>
   <int value="1" label="Corruption"/>