Don't crash when trying to create an ExtensionSyncData from invalid SyncData.

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 aa061209bc5262ff46c0cc4311f46b985a4cbcbf..b22a5f915890ba1aa1aa126b06aa0afb6ff5b136 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8461,6 +8461,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Extensions.BadSyncDataReason" enum="BadSyncDataReason">
+  <owner>yoz@chromium.org</owner>
+  <summary>
+    The reason a valid ExtensionSyncData could not be parsed from a SyncData
+    received from sync.
+  </summary>
+</histogram>
+
 <histogram name="Extensions.CheckForExternalUpdatesTime">
   <owner>rkaplow@chromium.org</owner>
   <summary>
@@ -44787,6 +44795,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="2" label="Failure"/>
 </enum>
 
+<enum name="BadSyncDataReason" type="int">
+  <int value="0" label="Bad extension ID"/>
+  <int value="1" label="Bad version"/>
+  <int value="2" label="Bad update URL"/>
+  <int value="3" label="No ExtensionSpecifics"/>
+</enum>
+
 <enum name="BaseRelocationType" type="int">
   <int value="0" label="IMAGE_REL_BASED_ABSOLUTE"/>
   <int value="1" label="IMAGE_REL_BASED_HIGH"/>