Small refactor to CompoundAssignmentNormalizer.

CompoundAssignmentNormalizer allows subclasses to choose different
strategies for creating locals.

By default CompoundAssignmentNormalizer creates uninitialized locals
all with the same name; assuming that equal names do not imply same
variable.

Subclasses might decide to create unique names or initialized
locals instead to serve different scenarios.

Change-Id: Ia19e19f154e6f2490af6b8729e71e73f6a6acd24
Adds methods to StubScheduler to execute the recorded commands somewhat similarly to the real SchedulerImpl.

Change-Id: I863c31c4a72a1a79064ad8a31e18c9efde5d63ef
Review-Link: https://gwt-review.googlesource.com/#/c/4540/
Change getSubRowElement's visibility to protected

Change-Id: Id3aa37d67b09b5048481d7ff10d38ff009c7ed4b
Merge remote-tracking branch 'upstream/master'

Updating master