Adding a SQL implementation of the backing store for previews opt outs

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 f071f404b2fae7d7069e16ee95f6bffb5a60866e..441a48d0484a9fc4f3bcd602b018fb3bb7f8f5d2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -108127,20 +108127,21 @@ value.
   <suffix name="AppCache" label="AppCache"/>
   <suffix name="BookmarkImages" label="BookmarkImages"/>
   <suffix name="Cookie" label="Cookie"/>
   <suffix name="DatabaseTracker" label="DatabaseTracker"/>
   <suffix name="DomainBoundCerts" label="DomainBoundCerts"/>
   <suffix name="DOMStorageDatabase" label="DOMStorageDatabase"/>
   <suffix name="History" label="History"/>
   <suffix name="OfflinePageMetadata" label="OfflinePageMetadata"/>
   <suffix name="Passwords" label="Passwords"/>
   <suffix name="Predictor" label="Predictor"/>
+  <suffix name="PreviewsOptOut" label="PreviewsOptOut"/>
   <suffix name="Quota" label="Quota"/>
   <suffix name="Shortcuts" label="Shortcuts"/>
   <suffix name="SyncDirectory" label="SyncDirectory"/>
   <suffix name="Text" label="Text (obsolete 7/24/13)"/>
   <suffix name="Thumbnail" label="Thumbnail"/>
   <suffix name="TopSites" label="TopSites"/>
   <suffix name="Web" label="Web"/>
   <affected-histogram name="Sqlite.AutoCommitTime"/>
   <affected-histogram name="Sqlite.CommitTime"/>
   <affected-histogram name="Sqlite.Error"/>