Replace ASSERT(false) by RTC_NOTREACHED().

This cl was produced by

  git grep -l 'ASSERT(false)' |\
    xargs -n1 sed -i 's/ASSERT(false)/RTC_NOTREACHED()/'

followed by additional includes of base/checks.h in affected files,
git cl format to adjust spacing in webrtc/base/transformadapter.cc.
Finally, to make presubmit happy, one unnamed TODO marker was deleted
in that file.

This is a step towards deletion of base/common.h.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2625003003
Cr-Commit-Position: refs/heads/master@{#16009}
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 4f731da..1d85e73 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -32,6 +32,7 @@
 #include "webrtc/api/videotrack.h"
 #include "webrtc/base/arraysize.h"
 #include "webrtc/base/bind.h"
+#include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/stringencode.h"
 #include "webrtc/base/stringutils.h"
@@ -399,7 +400,7 @@
     case PeerConnectionInterface::kAll:
       return cricket::CF_ALL;
     default:
-      ASSERT(false);
+      RTC_NOTREACHED();
   }
   return cricket::CF_NONE;
 }