Add the Sync.Attachments.StoreInitResult histogram.

BUG=436134

Review URL: https://codereview.chromium.org/751313005

Cr-Commit-Position: refs/heads/master@{#307943}

2 files changed, 10 insertions, 3 deletions

diff --git a/sync/api/attachments/attachment_store.h b/sync/api/attachments/attachment_store.h
index d6d0d39..b289723 100644
--- a/sync/api/attachments/attachment_store.h
+++ b/sync/api/attachments/attachment_store.h
@@ -33,11 +33,15 @@ class SYNC_EXPORT AttachmentStoreBase {
   // TODO(maniscalco): Consider udpating Read and Write methods to support
   // resumable transfers (bug 353292).
 
+  // The result status of an attachment store operation.
+  // Do not re-order or delete these entries; they are used in a UMA histogram.
   enum Result {
-    SUCCESS,            // No error, all completed successfully.
-    UNSPECIFIED_ERROR,  // An unspecified error occurred for one or more items.
-    STORE_INITIALIZATION_FAILED,  // AttachmentStore initialization failed.
+    SUCCESS = 0,            // No error, all completed successfully.
+    UNSPECIFIED_ERROR = 1,  // An unspecified error occurred for >= 1 item.
+    STORE_INITIALIZATION_FAILED = 2,  // AttachmentStore initialization failed.
+    // When adding a value here, you must increment RESULT_SIZE below.
   };
+  const int RESULT_SIZE = 10; // Size of the Result enum; used for histograms.
 
   typedef base::Callback<void(const Result&)> InitCallback;
   typedef base::Callback<void(const Result&,
diff --git a/sync/internal_api/attachments/on_disk_attachment_store.cc b/sync/internal_api/attachments/on_disk_attachment_store.cc
index 309e610..dc51508 100644
--- a/sync/internal_api/attachments/on_disk_attachment_store.cc
+++ b/sync/internal_api/attachments/on_disk_attachment_store.cc
@@ -8,6 +8,7 @@
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
 #include "base/sequenced_task_runner.h"
 #include "sync/internal_api/attachments/proto/attachment_store.pb.h"
 #include "sync/internal_api/public/attachments/attachment_util.h"
@@ -92,6 +93,8 @@ OnDiskAttachmentStore::~OnDiskAttachmentStore() {
 void OnDiskAttachmentStore::Init(const InitCallback& callback) {
   DCHECK(CalledOnValidThread());
   Result result_code = OpenOrCreate(path_);
+  UMA_HISTOGRAM_ENUMERATION("Sync.Attachments.StoreInitResult",
+                            result_code, RESULT_SIZE);
   callback_task_runner_->PostTask(FROM_HERE, base::Bind(callback, result_code));
 }