Add LayoutTests for WebCrypto's ECDH algorithm.

LayoutTests/crypto/ecdh-generate-key-expected.txt

Index: LayoutTests/crypto/ecdh-generate-key-expected.txt
diff --git a/LayoutTests/crypto/ecdsa-generate-key-expected.txt b/LayoutTests/crypto/ecdh-generate-key-expected.txt
similarity index 68%
copy from LayoutTests/crypto/ecdsa-generate-key-expected.txt
copy to LayoutTests/crypto/ecdh-generate-key-expected.txt
index 92573e0db63681f6886825c02acf37bda32b51c9..f966fa9ec363e051b076cc46c429b38003c7c724 100644
--- a/LayoutTests/crypto/ecdsa-generate-key-expected.txt
+++ b/LayoutTests/crypto/ecdh-generate-key-expected.txt
@@ -1,4 +1,4 @@
-Test generating an EC key pair for ECDSA.
+Test generating an EC key pair for ECDH.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
@@ -6,13 +6,13 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 Generating a key pair...
 PASS keyPair.toString() is '[object Object]'
 PASS keyPair.publicKey.type is 'public'
-PASS keyPair.publicKey.algorithm.name is 'ECDSA'
+PASS keyPair.publicKey.algorithm.name is 'ECDH'
 PASS keyPair.publicKey.algorithm.namedCurve is 'P-256'
-PASS keyPair.publicKey.usages is ["verify"]
+PASS keyPair.publicKey.usages is []
 PASS keyPair.privateKey.type is 'private'
-PASS keyPair.privateKey.algorithm.name is 'ECDSA'
+PASS keyPair.privateKey.algorithm.name is 'ECDH'
 PASS keyPair.privateKey.algorithm.namedCurve is 'P-256'
-PASS keyPair.privateKey.usages is ["sign"]
+PASS keyPair.privateKey.usages is ["deriveBits"]
 
 Testing that custom attributes on keys survive garbage collection...
 PASS keyPair.publicKey.foo is 'bar'