If the intent's package equals to the app's package, this intent
will be allowed to startActivityForResult.
But this check is unsafe, because if the component of this intent
is set, the package field will just be ignored. So if we set the
component to any activity we like and set package to the app's
package, it will pass the assertSafeToStartCustomActivity check
and now we can launch anywhere.
Bug: 223578534
Test: robotest and manual verify
Change-Id: I40496105bae313fe5cff2a36dfe329c1e2b5bbe4
90e095dbe3