WebCrypto: Add the KeyPair interface.

Source/modules/modules.gypi

 {
   'variables': {
     # Experimental hooks for embedder to provide extra IDL and source files.
     #
     # Note: this is not a supported API. If you rely on this, you will be broken
     # from time to time as the code generator changes in backward incompatible
     # ways.
     'extra_blink_module_idl_files': [],
     'extra_blink_module_files': [],
 
     'deprecated_perl_modules_idl_files': [
       '<@(extra_blink_module_idl_files)',
       'crypto/AesCbcParams.idl',
       'crypto/AesKeyGenParams.idl',
       'crypto/Algorithm.idl',
       'crypto/Crypto.idl',
       'crypto/HmacKeyParams.idl',
       'crypto/HmacParams.idl',
       'crypto/Key.idl',
+      'crypto/KeyPair.idl',
       'crypto/RsaKeyGenParams.idl',
       'crypto/RsaSsaParams.idl',
       'crypto/SubtleCrypto.idl',
       'crypto/WorkerCrypto.idl',
       'device_orientation/DeviceAcceleration.idl',
       'device_orientation/DeviceMotionEvent.idl',
       'device_orientation/DeviceOrientationEvent.idl',
       'device_orientation/DeviceRotationRate.idl',
       'encoding/TextDecoder.idl',
       'encoding/TextEncoder.idl',
@@ skipping 187 matching lines @@
       'crypto/CryptoResult.cpp',
       'crypto/CryptoResult.h',
       'crypto/DOMWindowCrypto.cpp',
       'crypto/DOMWindowCrypto.h',
       'crypto/HmacKeyParams.cpp',
       'crypto/HmacKeyParams.h',
       'crypto/HmacParams.cpp',
       'crypto/HmacParams.h',
       'crypto/Key.cpp',
       'crypto/Key.h',
+      'crypto/KeyPair.cpp',
+      'crypto/KeyPair.h',
       'crypto/NormalizeAlgorithm.cpp',
       'crypto/NormalizeAlgorithm.h',
       'crypto/RsaKeyGenParams.cpp',
       'crypto/RsaKeyGenParams.h',
       'crypto/RsaSsaParams.cpp',
       'crypto/RsaSsaParams.h',
       'crypto/SubtleCrypto.cpp',
       'crypto/SubtleCrypto.h',
       'crypto/WorkerCrypto.cpp',
       'crypto/WorkerCrypto.h',
@@ skipping 520 matching lines @@
       'indexeddb/IDBKeyPathTest.cpp',
       'indexeddb/IDBRequestTest.cpp',
       'indexeddb/IDBTransactionTest.cpp',
       'websockets/WebSocketDeflaterTest.cpp',
       'websockets/WebSocketExtensionDispatcherTest.cpp',
       'websockets/WebSocketExtensionParserTest.cpp',
       'websockets/WebSocketPerMessageDeflateTest.cpp',
     ],
   },
 }