Bug 1587164 - Avoid left shift of negative value in TimestampWrapAroundHandler; r=bwc

The code for handling backwards wraps left shifts num_wrap_ - 1. If
num_wrap_ is zero, this results in a left shift of a negative value which
is undefined behaviour. This modifies the code to avoid the shift at the cost
of an extra multiplication.

Differential Revision: https://phabricator.services.mozilla.com/D49609

--HG--
extra : moz-landing-system : lando

media/webrtc/trunk/webrtc/rtc_base/timeutils.cc

@@ -139,7 +139,7 @@ int64_t TimestampWrapAroundHandler::Unwrap(uint32_t ts) {
       ++num_wrap_;
   } else if ((ts - last_ts_) > 0xf0000000) {
     // Backwards wrap. Unwrap with last wrap count and don't update last_ts_.
-    return ts + ((num_wrap_ - 1) << 32);
+    return ts + (num_wrap_ - 1)*((int64_t)1 << 32);
   }
 
   last_ts_ = ts;