[webcrypto] Reject failed operations with a DOMException rather than null.

LayoutTests/crypto/resources/common.js

-function shouldBeTypeError(toEval)
+function logError(error)
 {
-    var value = eval(toEval);
-    if (value instanceof TypeError) {
-        testPassed(toEval + " is: " + value.toString());
-    } else {
-        testFailed(toEval + " is not a TypeError: " + value);
-    }
+    debug("error is: " + error.toString());
 }
 
 // Verifies that the given "bytes" holds the same value as "expectedHexString".
 // "bytes" can be anything recognized by "bytesToHexString()".
 function bytesShouldMatchHexString(testDescription, expectedHexString, bytes)
 {
     expectedHexString = "[" + expectedHexString.toLowerCase() + "]";
     var actualHexString = "[" + bytesToHexString(bytes) + "]";
 
     if (actualHexString === expectedHexString) {
@@ skipping 87 matching lines @@
         debug("Serialized key bytes: " + bytesToHexString(serializedWithoutVersion));
     }
 }
 
 function shouldEvaluateAs(actual, expectedValue)
 {
     if (typeof expectedValue == "string")
         return shouldBeEqualToString(actual, expectedValue);
     return shouldEvaluateTo(actual, expectedValue);
 }