Add support for content-hint value "text"

This involves treating it just like "detailed", for now.
At a later stage we might want to modify codec parameters for it.

Bug: chromium:852701
Change-Id: I24678e1f7711bf03ca22273afaaf338e9e3ba1fe
Reviewed-on: https://webrtc-review.googlesource.com/83582
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Peter Boström <pbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23701}
diff --git a/pc/rtpsender.cc b/pc/rtpsender.cc
index f3bf970..13e0e1d 100644
--- a/pc/rtpsender.cc
+++ b/pc/rtpsender.cc
@@ -549,6 +549,7 @@
       options.is_screencast = false;
       break;
     case VideoTrackInterface::ContentHint::kDetailed:
+    case VideoTrackInterface::ContentHint::kText:
       options.is_screencast = true;
       break;
   }