While working on JDK-8349088 I realized that `CodeBlob::is_buffer_blob()` is incorrectly used in few places because BufferBlob is not "leaf" class. All other `is_*()` methods are fine because they correspond to "leaf" subclasses.

The method is mostly used for prints and statistic. Like in `CodeBlob::dump_for_addr()` and `CodeCache::print_internals()`.

The only problematic place is in `CodeBlobCollector::do_blob()` where `if (cb->is_buffer_blob() && strcmp(cb->name(), "vtable chunks") == 0)` should be replaces with `(cb->is_vtable_blob())`.
That code works anyway because `CodeBlobCollector::do_vtable_stub()` is called first and `CodeBlobCollector::do_blob()` skips blobs which are already recorded.