Replace RTC_DCHECK(false) with RTC_NOTREACHED().

Bulk of changes done using

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

peerconnection.cc also used RTC_DCHECK(false && "msg") in two places,
which were updated manually.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2623313004
Cr-Commit-Position: refs/heads/master@{#16026}
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 2f21e0c..1a29e55 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -327,7 +327,7 @@
     default:
       // We shouldn't get to this point with an invalid service_type, we should
       // have returned an error already.
-      RTC_DCHECK(false) << "Unexpected service type";
+      RTC_NOTREACHED() << "Unexpected service type";
       return RTCErrorType::INTERNAL_ERROR;
   }
   return RTCErrorType::NONE;
@@ -548,7 +548,7 @@
   std::string cname;
   if (!rtc::CreateRandomString(kRtcpCnameLength, &cname)) {
     LOG(LS_ERROR) << "Failed to generate CNAME.";
-    RTC_DCHECK(false);
+    RTC_NOTREACHED();
   }
   return cname;
 }
@@ -1617,7 +1617,7 @@
       break;
     }
     default:
-      RTC_DCHECK(false && "Not implemented");
+      RTC_NOTREACHED() << "Not implemented";
       break;
   }
 }
@@ -2042,7 +2042,7 @@
   } else if (media_type == cricket::MEDIA_TYPE_VIDEO) {
     CreateVideoReceiver(stream, track_id, ssrc);
   } else {
-    RTC_DCHECK(false && "Invalid media type");
+    RTC_NOTREACHED() << "Invalid media type";
   }
 }