MediaSession: Fix a crash when calling seek(0) on debug build

It is an assert error. According to the method's description[1], we
should assert that it is NOT zero.

Bug: none
Change-Id: I3da2e4006a147d256b4980878ae279dd9b4ee548
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2519535Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Jinho Bang <jinho.bang@samsung.com>
Cr-Commit-Position: refs/heads/master@{#823968}

content/public/android/java/src/org/chromium/content/browser/MediaSessionImpl.java

@@ -69,7 +69,7 @@ public class MediaSessionImpl extends MediaSession {
 
     @Override
     public void seek(long millis) {
-        assert millis == 0 : "Attempted to seek by an unspecified number of milliseconds";
+        assert millis != 0 : "Attempted to seek by an unspecified number of milliseconds";
         MediaSessionImplJni.get().seek(mNativeMediaSessionAndroid, MediaSessionImpl.this, millis);
     }