Disk cache: Add support for an extra data stream for each cache entry....

net/data/cache_tests/bad_rankings/contents.txt

+Index header:
+num_entries: 2
+num_bytes: 27
+this_id: 1
+table_len: 64k
+
+head: 0x90000001
+tail: 0x90000000
+
+Address: 0xa0010002
+Address: 0xa0010003
+
+-------------------------------
+
+entry:
+Address: 0xa0010002
+hash: 0x687d1422
+next: 0
+rankings_node: 0x90000000
+key_len: 13
+long_key: 0
+data_size: 0's
+data_addr: 0's
+key: "the first key"
+
+rankings:
+Address: 0x90000000
+next: 0x90000000
+prev: 0                 <------ wrong
+contents: 0xa0010002
+dirty: 0
+pointer: 0
+
+-------------------------------
+
+entry:
+Address: 0xa0010003
+hash: 0x63909ecb
+next: 0
+rankings_node: 0x90000001
+key_len: 14
+long_key: 0
+data_size: 0's
+data_addr: 0's
+key: "some other key"
+
+rankings:
+Address: 0x90000001
+next: 0x90000000
+prev: 0x90000001
+contents: 0xa0010003
+dirty: 0
+pointer: 0
+
+================================
+
+Generated with:
+
+disk_cache::Entry *entry;
+ASSERT_TRUE(cache_->CreateEntry("the first key", &entry));
+entry->Close();
+
+ASSERT_TRUE(cache_->CreateEntry("some other key", &entry));   <---- Edit value*
+entry->Close();
+
+* Edit the value with the debugger before it is saved to disk.