[MSE][MAC]xhr cache corrupted under some circumstances.

• Component: WebCore Misc.
• Status: NEW ---

When we try to execute some youtube MSE tests within webkit (SAFARI 8.0.3) or webkit tip,
http://yt-dash-mse-test.commondatastorage.googleapis.com/unit-tests/tip.html

the test fails the second time, because a request is made via a HTTPRequest for a file which was downloaded earlier with a different size.

In the url above, click on test 14 (AppendAudio), once the test is over it becomes green. 
Then, click on test 16 (AbortAudio), upon completion it also becomes green.
At last, click again on test 14 (AppendAudio) and this time it is red.

In the result text box, we can see that a file of 200000 bytes was downloaded where it shall have been 1MB bytes. A wireshark capture confirms that the file was retrieved from the cache and not from the network.

[Radar WebKit Bug Importer]

<rdar://problem/20048268>