Add uma stats to help evaluate the impact of changes to the quota allocation logic.

content/browser/cache_storage/cache_storage_blob_to_disk_cache.cc

Index: content/browser/cache_storage/cache_storage_blob_to_disk_cache.cc
diff --git a/content/browser/cache_storage/cache_storage_blob_to_disk_cache.cc b/content/browser/cache_storage/cache_storage_blob_to_disk_cache.cc
index a375f8c140c634ae79ff0ad72cf1d9c0274c03c3..10c0fa672d8c8bfa70a6702c6230cc19d26542c1 100644
--- a/content/browser/cache_storage/cache_storage_blob_to_disk_cache.cc
+++ b/content/browser/cache_storage/cache_storage_blob_to_disk_cache.cc
@@ -12,6 +12,7 @@
 #include "net/url_request/url_request_context_getter.h"
 #include "storage/browser/blob/blob_data_handle.h"
 #include "storage/browser/blob/blob_url_request_job_factory.h"
+#include "storage/common/storage_histograms.h"
 
 namespace content {
 
@@ -137,7 +138,8 @@ void CacheStorageBlobToDiskCache::DidWriteDataToEntry(int expected_bytes,
     RunCallbackAndRemoveObserver(false);
     return;
   }
-
+  if (rv > 0)
+    storage::RecordBytesWritten("DiskCache.CacheStorage", rv);
   cache_entry_offset_ += rv;
   ReadFromBlob();
 }