1) assertInstanceOf(o, Foo, Bar) used to produce this error message:

Failure: expected <o> is not an instance of <Foo> but of < Bar>> found <undefined>

Fixed:

Failure: <o> is not an instance of <Foo> but of <Bar>

2) assertDoesNotThrow("throw 1") used to produce this error message:

Failure: expected <threw an exception: > found <1>

Fixed:

Failure: threw an exception: 1

3) assertDoesNotThrow("...", SomeError) was not doing what you'd
think it does, so removed the last parameter.

BUG=

Review-Url: https://codereview.chromium.org/2424743003
Cr-Commit-Position: refs/heads/master@{#40347}