Roll WebRTC from fa54364cea0b to 78e9acd96726 (3 revisions)

https://webrtc.googlesource.com/src.git/+log/fa54364cea0b..78e9acd96726

2020-09-16 kwiberg@webrtc.org UntypedFunction: Add unit tests and fix a few issues
2020-09-16 mbonadei@webrtc.org Clobber iOS builders.
2020-09-16 lndmrk@webrtc.org Explicitly enable CDEF

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/webrtc-chromium-autoroll
Please CC webrtc-chromium-sheriffs-robots@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Bug: None
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I94f8871f30421af39b1dba6ebcae6065e579df3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2414528Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#807563}

DEPS

@@ -1471,7 +1471,7 @@ deps = {
   },
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + 'fa54364cea0be4ce3862bc1058ab58b935820de1',
+    Var('webrtc_git') + '/src.git' + '@' + '78e9acd9672649f2660ebd054bd1ce16828d992f',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),