[Android][WebSignin] Remove the usage of ChromeActivity in addAccount()

This CL removes the usage of ChromeActivity in
AccountPickerDelegate#addAccount() for context.

Bug: 1125068
Change-Id: I73b82d63352d7d12243bbd9d28ec06455e24c270
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2395755Reviewed-by: Tanmoy Mollik <triploblastic@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804787}

chrome/android/java/src/org/chromium/chrome/browser/signin/account_picker/AccountPickerDelegate.java

@@ -108,7 +108,7 @@ public class AccountPickerDelegate implements WebSigninBridge.Listener {
                     } else {
                         // AccountManagerFacade couldn't create intent, use SigninUtils to open
                         // settings instead.
-                        SigninUtils.openSettingsForAllAccounts(mChromeActivity);
+                        SigninUtils.openSettingsForAllAccounts(mWindowAndroid.getContext().get());
                     }
                 });
     }