media: Fix expiry time convertion from base::Time to JS time

This is broken by https://codereview.chromium.org/2593073002/ where the
behavior of converting a null base::Time to JS time (double) has been
changed. We are discussing how to fix the base::Time API more properly.
For now, this check should work.

BUG=679079
TEST=Manually tested. I'll add auto tests later.

Review-Url: https://codereview.chromium.org/2650033007
Cr-Commit-Position: refs/heads/master@{#446246}

media/blink/webcontentdecryptionmodulesession_impl.cc

@@ -495,7 +495,11 @@ void WebContentDecryptionModuleSessionImpl::OnSessionKeysChange(
 void WebContentDecryptionModuleSessionImpl::OnSessionExpirationUpdate(
     base::Time new_expiry_time) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  client_->expirationChanged(new_expiry_time.ToJsTime());
+  // The check works around an issue in base::Time that converts null base::Time
+  // to |1601-01-01 00:00:00 UTC| in ToJsTime(). See http://crbug.com/679079
+  client_->expirationChanged(new_expiry_time.is_null()
+                                 ? std::numeric_limits<double>::quiet_NaN()
+                                 : new_expiry_time.ToJsTime());
 }
 
 void WebContentDecryptionModuleSessionImpl::OnSessionClosed() {

third_party/WebKit/Source/modules/encryptedmedia/MediaKeySession.cpp

@@ -959,9 +959,7 @@ void MediaKeySession::expirationChanged(double updatedExpiryTimeInMS) {
 
   // 3. If the new expiration time is not NaN, let expiration time be the
   //    new expiration time in milliseconds since 01 January 1970 UTC.
-  //    (Note that Chromium actually passes 0 to indicate no expiry.)
-  // FIXME: Get Chromium to pass NaN.
-  if (!std::isnan(updatedExpiryTimeInMS) && updatedExpiryTimeInMS != 0.0)
+  if (!std::isnan(updatedExpiryTimeInMS))
     expirationTime = updatedExpiryTimeInMS;
 
   // 4. Set the session's expiration attribute to expiration time.