Prevent apps from spamming addAccountExplicitly.

See comment here for the discussion on solution
https://b.corp.google.com/issues/169762606#comment14

Change-Id: If212df3a3b7be1de0fb26b8e88b2fcbb8077c253

Bug: 169762606

core/java/android/accounts/Account.java

@@ -31,6 +31,7 @@ import android.util.Log;
 
 import com.android.internal.annotations.GuardedBy;
 
+import java.util.Objects;
 import java.util.Set;
 
 /**
@@ -86,6 +87,12 @@ public class Account implements Parcelable {
         if (TextUtils.isEmpty(type)) {
             throw new IllegalArgumentException("the type must not be empty: " + type);
         }
+        if (name.length() > 200) {
+            throw new IllegalArgumentException("account name is longer than 200 characters");
+        }
+        if (type.length() > 200) {
+            throw new IllegalArgumentException("account type is longer than 200 characters");
+        }
         this.name = name;
         this.type = type;
         this.accessId = accessId;

services/core/java/com/android/server/accounts/AccountManagerService.java

@@ -1830,6 +1830,11 @@ public class AccountManagerService
                                 + ", skipping since the account already exists");
                         return false;
                     }
+                    if (accounts.accountsDb.findAllDeAccounts().size() > 100) {
+                        Log.w(TAG, "insertAccountIntoDatabase: " + account.toSafeString()
+                                + ", skipping since more than 50 accounts on device exist");
+                        return false;
+                    }
                     long accountId = accounts.accountsDb.insertCeAccount(account, password);
                     if (accountId < 0) {
                         Log.w(TAG, "insertAccountIntoDatabase: " + account.toSafeString()