weblayer: revise comment for ScrollOffsetCallback

It wasn't clear whether the supplied parameter is a delta or absolute
value. Hopefully this clears that up.

BUG=none
TEST=none

Change-Id: Ic0921d209c1c11f125cdc6b8821d9bf265c8cd77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487683Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819074}

weblayer/public/java/org/chromium/weblayer/ScrollOffsetCallback.java

@@ -19,7 +19,10 @@ package org.chromium.weblayer;
  */
 public abstract class ScrollOffsetCallback {
     /**
-     * Called when the scroll offset of the content of a Tab changes.
+     * Called when the vertical scroll location of the content of a Tab changes.
+     *
+     * @param scrollLocation The new vertical location. More specifically, the 'scrollTop' html
+     * property.
      */
-    public abstract void onVerticalScrollOffsetChanged(int scrollOffset);
+    public abstract void onVerticalScrollOffsetChanged(int scrollLocation);
 }