Credential Manager: Migrate to WebView client-based approach.

public/platform/Platform.h

Index: public/platform/Platform.h
diff --git a/public/platform/Platform.h b/public/platform/Platform.h
index 6fc99347be5d7cf4470b69a2e5efeb831c9e1f65..8538892d297ab9e4ddacf128d7d9c15bdd1f19e6 100644
--- a/public/platform/Platform.h
+++ b/public/platform/Platform.h
@@ -66,7 +66,6 @@ class WebClipboard;
 class WebCompositorSupport;
 class WebConvertableToTraceFormat;
 class WebCookieJar;
-class WebCredentialManager;
 class WebCrypto;
 class WebDatabaseObserver;
 class WebDiscardableMemory;
@@ -171,10 +170,6 @@ public:
     // Must return non-null.
     virtual WebBlobRegistry* blobRegistry() { return 0; }
 
-    // Credential Management -----------------------------------------------
-
-    virtual WebCredentialManager* credentialManager() { return 0; }
-
     // Database ------------------------------------------------------------
 
     // Opens a database file; dirHandle should be 0 if the caller does not need