[webcrypto] Match the error handling defined by the spec.

LayoutTests/crypto/sign-verify.html

Index: LayoutTests/crypto/sign-verify.html
diff --git a/LayoutTests/crypto/sign-verify.html b/LayoutTests/crypto/sign-verify.html
index 342a2ba83f573ea582c4ec6b7cf4301da83ada3f..79b791d31cb40126d57b798109650e60711cb64a 100644
--- a/LayoutTests/crypto/sign-verify.html
+++ b/LayoutTests/crypto/sign-verify.html
@@ -140,17 +140,17 @@ allTests.push(importTestKeys().then(function(importedKeys) {
     shouldThrow("crypto.subtle.sign({name: 'RSAES-PKCS1-v1_5'}, keys.hmacSha1, data)");
 
     // Key's algorithm must match.
-    shouldThrow("crypto.subtle.sign({name: 'hmac', hash: {name: 'sha-256'}}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac', hash: {name: 'sha-256'}}, keys.hmacSha1, data)");
 
     // ---------------------------------------------------
     // HMAC normalization failures (HmacParams)
     // ---------------------------------------------------
-    shouldThrow("crypto.subtle.sign({name: 'hmac'}, keys.hmacSha1, data)");
-    shouldThrow("crypto.subtle.sign({name: 'hmac', hash: 3}, keys.hmacSha1, data)");
-    shouldThrow("crypto.subtle.sign({name: 'hmac', hash: null}, keys.hmacSha1, data)");
-    shouldThrow("crypto.subtle.sign({name: 'hmac', hash: {}}, keys.hmacSha1, data)");
-    shouldThrow("crypto.subtle.sign({name: 'hmac', hash: {name: 'foo'}}, keys.hmacSha1, data)");
-    shouldThrow("crypto.subtle.sign({name: 'hmac', hash: {name: 'AES-CBC'}}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac'}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac', hash: 3}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac', hash: null}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac', hash: {}}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac', hash: {name: 'foo'}}, keys.hmacSha1, data)");
+    shouldRejectPromiseWithNull("crypto.subtle.sign({name: 'hmac', hash: {name: 'AES-CBC'}}, keys.hmacSha1, data)");
 }));
 
 // -------------------------------------------------