Update WebSettings useragent docs.

Update the WebSettings.setUserAgentString API docs to explicitly specify
the effect it has on user agent client hints and related JS APIs.

This is not a behaviour change for WebView, just making the docs
describe what already happens.

Test: make offline-sdk-docs
Change-Id: I2db282efc4ee42b931824175abe627e871c4a86c
1 file changed