If data is successfully written to an entry (via WriteData) the entry size should increase - it does not.

This is a result of a recent change https://codereview.chromium.org/2957133002.

Here is a modification to an existing unit test that demonstrates this problem:

void DiskCacheBackendTest::BackendCalculateSizeOfAllEntries() {
  ...
  const std::string key = "A Key";
  {
    disk_cache::Entry* entry;
    EXPECT_NE(net::OK, OpenEntry(key, &entry));
    ASSERT_THAT(CreateEntry(key, &entry), IsOk());
    ASSERT_TRUE(nullptr != entry);
    entry->Close();
  }
  int size_after_write = CalculateSizeOfAllEntries();
  EXPECT_GT(size_after_write, 0);
  // Now write some data at a given index.
  {
    disk_cache::Entry* entry;
    ASSERT_THAT(OpenEntry(key, &entry), IsOk());
    ASSERT_TRUE(nullptr != entry);
    const std::string data = "SideDataSample";
    scoped_refptr<net::IOBuffer> buffer(new net::StringIOBuffer(data));
    const int buf_length = data.length();
    const int index = 0;
    EXPECT_EQ(buf_length, WriteData(entry, index, 0 /* offset */, buffer.get(),
                                    buf_length, false));
    entry->Close();
    EXPECT_GT(CalculateSizeOfAllEntries(), size_after_write)
        << "Writing " << buf_length << " bytes of data to index " << index
        << " did not increase the backend size.";
  }
}