WebCrypto: Add crypto.subtle.verify() to the platform interfaces.

LayoutTests/crypto/sign-verify-expected.txt

Index: LayoutTests/crypto/sign-verify-expected.txt
diff --git a/LayoutTests/crypto/sign-verify-expected.txt b/LayoutTests/crypto/sign-verify-expected.txt
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+++ b/LayoutTests/crypto/sign-verify-expected.txt
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+Tests cypto.subtle.sign and crypto.subtle.verify
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS crypto.subtle.verify(hmacSha1, hmacSha1Key, null) threw exception TypeError: Type error.
+PASS crypto.subtle.verify(hmacSha1, hmacSha1Key, 'a') threw exception TypeError: Type error.
+PASS crypto.subtle.verify(hmacSha1, hmacSha1Key, []) threw exception TypeError: Type error.
+PASS signResult.byteLength is 17
+PASS verifyResult1 is true
+PASS verifyResult2 is false
+PASS successfullyParsed is true
+
+TEST COMPLETE
+