Add fudge to duration tests

Merge from Widevine repo of http://go/wvgerrit/125046

Add some extra fudge to the termination time. This assumes that flaky
tests were caused by roundoff error.

Bug: 175741647
Change-Id: I9bcc86f9b9540e5985df647dd1b5c5d439556e2b

libwvdrmengine/cdm/core/test/duration_use_case_test.cpp

@@ -358,8 +358,10 @@ class CdmDurationTest : public WvCdmTestBaseWithEngine,
   // this tests a cyan bar with a black X. This assumes that |cutoff| is before
   // |stop|. Both |start| and |cutoff| are system times.
   void TerminatePlayback(uint64_t start, uint64_t cutoff) {
-    ASSERT_LT(start, cutoff);
-    AllowPlayback(start, cutoff);
+    // We subtract some fudge from the cutoff to account for possible round off
+    // error when computing the playback window.
+    ASSERT_LT(start, cutoff - kFudge);
+    AllowPlayback(start, cutoff - kFudge);
     SleepUntil(cutoff + kFudge);
     FailDecrypt();
   }