Bug 1600814 - Don't call setFixedBottomOffset if the offset value is not changed. r=geckoview-reviewers,snorp

Differential Revision: https://phabricator.services.mozilla.com/D55577

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

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java

@@ -5377,6 +5377,10 @@ public class GeckoSession implements Parcelable {
 
 
     /* package */ void setFixedBottomOffset(final int offset) {
+        if (mFixedBottomOffset == offset) {
+            return;
+        }
+
         mFixedBottomOffset = offset;
 
         if (mCompositorReady) {