BookmarkActivity used to take a pointer to a BookmarkModel, but that was changed in https://chromium-review.googlesource.com/c/chromium/src/+/1017323 to precompute whether the URL was bookmarked or not and take that as a BOOL.  This was done because the BookmarkActivity can potentially outlive the C++ BookmarkModel, which was leading to crashes in unittests.

Please confirm that it is ok to precompute the bookmarked state like this.  If it is important for the BookmarkActivity to continue having a pointer to the model, we can do that as well, but I chose to make the simpler change to start.

(If we need to keep the model, we will need to register as a BookmarkModelObserver and listen for "model destroyed" calls.  We should also dynamically disable the activity if the model is destroyed out from underneath it.)