Incorporate API changes for 'WebViewClient'

[ocram]

• https://developer.android.com/sdk/api_diff/23/changes/android.webkit.WebViewClient.html
• https://developer.android.com/sdk/api_diff/24/changes/android.webkit.WebViewClient.html
• https://developer.android.com/sdk/api_diff/26/changes/android.webkit.WebViewClient.html
• https://developer.android.com/sdk/api_diff/27/changes/android.webkit.WebViewClient.html