Colby recently observed opening files is sluggish. Digging into
profile data shows CM3 doing multiple relayouts if its internal
DOM during onShowView(), once for each method being invoked. Batch
these together into an operation() call, allowing CM3 to buffer
the updates and update its DOM only once.
Conflicts:
gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/SideBySide2.java
Change-Id: Iefbc112a37016c4031515b4422a02368e5af16c1
9e45db10c4