Credential Manager: Migrate to WebView client-based approach.

Source/modules/modules.gypi

 {
   'includes': [
     '../core/core_generated.gypi',
     'modules_generated.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
@@ skipping 289 matching lines @@
       'battery/BatteryManager.cpp',
       'battery/BatteryManager.h',
       'battery/BatteryStatus.cpp',
       'battery/BatteryStatus.h',
       'battery/NavigatorBattery.cpp',
       'battery/NavigatorBattery.h',
       'beacon/NavigatorBeacon.cpp',
       'beacon/NavigatorBeacon.h',
       'credentialmanager/Credential.cpp',
       'credentialmanager/Credential.h',
+      'credentialmanager/CredentialManagerClient.cpp',
+      'credentialmanager/CredentialManagerClient.h',
       'credentialmanager/CredentialsContainer.cpp',
       'credentialmanager/CredentialsContainer.h',
       'credentialmanager/FederatedCredential.cpp',
       'credentialmanager/FederatedCredential.h',
       'credentialmanager/LocalCredential.cpp',
       'credentialmanager/LocalCredential.h',
       'credentialmanager/NavigatorCredentials.cpp',
       'credentialmanager/NavigatorCredentials.h',
       'crypto/Crypto.cpp',
       'crypto/Crypto.h',
@@ skipping 697 matching lines @@
       'serviceworkers/ServiceWorkerContainerTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/NewWebSocketChannelImplTest.cpp',
       'websockets/WebSocketDeflaterTest.cpp',
       'websockets/WebSocketExtensionDispatcherTest.cpp',
       'websockets/WebSocketExtensionParserTest.cpp',
       'websockets/WebSocketPerMessageDeflateTest.cpp',
     ],
   },
 }