Implement HKDF for webcrypto

content/child/webcrypto/status.h

Index: content/child/webcrypto/status.h
diff --git a/content/child/webcrypto/status.h b/content/child/webcrypto/status.h
index c3331361ebb10c7c14d57986de98a53f51695dc4..c802e8ee0b6d0dbda5bfc213da42e6fd25e80975 100644
--- a/content/child/webcrypto/status.h
+++ b/content/child/webcrypto/status.h
@@ -256,6 +256,12 @@ class CONTENT_EXPORT Status {
   // The requested bit length for ECDH key derivation was too large.
   static Status ErrorEcdhLengthTooBig(unsigned int max_length_bits);
 
+  // The requested length for HKDF was too large.
+  static Status ErrorHkdfLengthTooLong();
+
+  // No length parameter was provided for deriveBits in hkdf.

[eroman, 2015/01/07 00:23:43]

nit: unclear what deriveBits references (as it is a not a function name at this
layer). In javascript it is a method (crypto.subtle.deriveBits()), however it is
not possible to pass no length to it so the comment doesn't make sense
interpreted that way either.

Howe about:

 No length parameter was provided for HKDF's Derive Bits operation.


(DeriveBits is the "operation", which backs both deriveBits() implementation and
deriveKey()).

[nharper, 2015/01/08 01:31:24]

Done.

+  static Status ErrorHkdfDeriveBitsLengthNotSpecified();
+
  private:
   enum Type { TYPE_ERROR, TYPE_SUCCESS };