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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/cache_storage/cache_storage_blob_to_disk_cache.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "net/base/io_buffer.h"
 #include "net/url_request/url_request_context.h"
 #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 {
 
 const int CacheStorageBlobToDiskCache::kBufferSize = 1024 * 512;
 
 CacheStorageBlobToDiskCache::CacheStorageBlobToDiskCache()
     : cache_entry_offset_(0),
       disk_cache_body_index_(0),
       buffer_(new net::IOBufferWithSize(kBufferSize)),
       weak_ptr_factory_(this) {
@@ skipping 105 matching lines @@
   if (bytes_read != net::ERR_IO_PENDING)
     OnReadCompleted(blob_request_.get(), bytes_read);
 }
 
 void CacheStorageBlobToDiskCache::DidWriteDataToEntry(int expected_bytes,
                                                       int rv) {
   if (rv != expected_bytes) {
     RunCallbackAndRemoveObserver(false);
     return;
   }
-
+  if (rv > 0)
+    storage::RecordBytesWritten("DiskCache.CacheStorage", rv);
   cache_entry_offset_ += rv;
   ReadFromBlob();
 }
 
 void CacheStorageBlobToDiskCache::RunCallbackAndRemoveObserver(bool success) {
   DCHECK(request_context_getter_);
 
   request_context_getter_->RemoveObserver(this);
   blob_request_.reset();
   callback_.Run(std::move(entry_), success);
 }
 
 }  // namespace content