Webcrypto: add layout tests for HKDF algorithm

LayoutTests/crypto/subtle/hkdf-failures-expected.txt

Index: LayoutTests/crypto/subtle/hkdf-failures-expected.txt
diff --git a/LayoutTests/crypto/subtle/hkdf-failures-expected.txt b/LayoutTests/crypto/subtle/hkdf-failures-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..d1db317b0408b12e85e7fdd830cb26d89f707790
--- /dev/null
+++ b/LayoutTests/crypto/subtle/hkdf-failures-expected.txt
@@ -0,0 +1,12 @@
+Test that HKDF does not support methods it should not support.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+
+HKDF does not support exportKey()...

[eroman, 2015/01/07 01:18:43]

Make this read what it is about to do:
   calling exportKey() for HKDF key...

[nharper, 2015/01/09 22:41:47]

Done.

+error is: NotSupportedError: Unsupported export key format for algorithm

[eroman, 2015/01/07 01:18:43]

This is an unexpected error message -- it should instead say the operation is
unsupported if we are to go by the spec's interpretation.

[eroman, 2015/01/09 03:16:01]

To clarify, this was just an FYI comment.

I expect you to leave it as-is in this changelist, however perhaps add a FIXME
linking to a bug.
(the exception type is correct, so it is spec compliant with or without a more
descriptive error message).

In fact I would prefer to keep any fix in a subsequent changelist.

+PASS successfullyParsed is true
+
+TEST COMPLETE
+