Chrome Version       : 50.0.2661.102 (64-bit)
URLs (if applicable) : N/A
Other browsers tested: Firefox, which had a different error
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari:
    Firefox:
         IE:

What steps will reproduce the problem?
(1) Go to a secure page (https)
(2) Open the developer console
(3) Enter and run the following code:

window.crypto.subtle.generateKey({name: "AES-CBC", length: 64}, true, []).then(function(k) {console.log("Generated a key.");}).catch(function(err) {console.log("Error: " + err.name);})

What is the expected result?

It displays "Error: OperationError"

What happens instead?

It displays "Error: SyntaxError"

Please provide any additional information below. Attach a screenshot if
possible.

The Web Cryptography API specification at https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html defines the generateKey operation in general in section 14.3.6, with specifics for AES-CBC in section 26.4.

In section 26.4, the first step is to make sure no requested usage is anything other than "encrypt", "decrypt", "wrapKey", or "unwrapKey", which this code passes. The second step is the check that the length parameter is 128, 192, or 256, which this code fails. The step says to throw an OperationError in this case.

Note that if a non-empty usages parameter is passed, as in the following code:

window.crypto.subtle.generateKey({name: "AES-CBC", length: 64}, true, ["encrypt"]).then(function(k) {console.log("Generated a key.");}).catch(function(err) {console.log("Error: " + err.name);})

then it does throw an OperationError as specified in section 26.4.

The second to last step of the general specification in section 14.3.6 checks that the result of the operation has a non-empty usages, and throws a SyntaxError if it does.

The code demonstrating the error has two problems with it: a bad length and an empty usages. The specification says that the bad length should be checked first, and cause an OperationError. Instead, a SyntaxError is thrown, which would be the correct response if the earlier error had not occurred.