UMA counts for corrupt cache db.

chrome/browser/chromeos/gdata/drive_cache_metadata.cc

Index: chrome/browser/chromeos/gdata/drive_cache_metadata.cc
===================================================================
--- chrome/browser/chromeos/gdata/drive_cache_metadata.cc	(revision 158657)
+++ chrome/browser/chromeos/gdata/drive_cache_metadata.cc	(working copy)
@@ -8,6 +8,7 @@
 
 #include "base/callback.h"
 #include "base/file_util.h"
+#include "base/metrics/histogram.h"
 #include "base/sequenced_task_runner.h"
 #include "chrome/browser/chromeos/gdata/drive.pb.h"
 #include "chrome/browser/chromeos/gdata/drive_file_system_util.h"
@@ -468,6 +469,7 @@
   // perhaps not other causes of failed DB::Open.
   if (!db_status.ok()) {
     DVLOG(1) << "Detected corrupt db";
+    UMA_HISTOGRAM_COUNTS("Drive.CorruptCacheDB", 1);

[satorux1, 2012/09/25 22:40:50]

I think we want to know success/failure ratio and failure reasons, so we want to
do something like:

enum {
  LOAD_SUCCESS,
  LOAD_FAILURE_CORRUPT_DB,
  LOAD_FAILURE_OTHER,
  LOAD_MAX_VALUE,
};

Then do:

UMA_HISTOGRAM_ENUMERATION("Drive.CacheMetadataLoading", LOAD_SUCCESS,
LOAD_MAX_VALUE)

I think we want to distinguish corruption from other errors, so I'd suggest
doing:

if (!db_status.ok()) {
  if (db_status.IsCorruption()) {
    LOG(WARNING) << "Detected corrupt db";
    UMA_HISTOGRAM_ENUMERATION("Drive.CacheMetadataLoading",
LOAD_FAILURE_CORRUPT_DB, LOAD_MAX_VALUE);
  } else {
    LOG(WARNING)  << "Failed to open db for unknown reason";
    UMA_HISTOGRAM_ENUMERATION("Drive.CacheMetadataLoading", LOAD_FAILURE_OTHER,
LOAD_MAX_VALUE);
  }

     const bool deleted = file_util::Delete(db_path, true);
     DCHECK(deleted);
     db_status = leveldb::DB::Open(options, db_path.value(), &level_db);