fixes #259, clone ast before mutation

fixes #259, clone ast before mutation

R=vsm@google.com

Committed: https://github.com/dart-lang/dev_compiler/commit/1c029d0902387059b16866c0c41489e7739ea89a

[Jennifer Messerly, 2015-07-21 19:58:45]

jmesserly@google.com changed reviewers:
+ vsm@google.com

[Jennifer Messerly, 2015-07-21 19:58:46]

https://codereview.chromium.org/1245013005/diff/40001/test/codegen/expect/sun...
File test/codegen/expect/sunflower/dom.js (right):

https://codereview.chromium.org/1245013005/diff/40001/test/codegen/expect/sun...
test/codegen/expect/sunflower/dom.js:1: dart_library.library('dom', window, /*
Imports */[
Note that "sunflower.js" imports this as "dom". I believe this was a symptom of
how we were avoiding visiting the compilation unit again. Ultimately this is an
issue with codegen_test, which is fixed in the relative path CL (and/or the work
in progress CL for async). So I'm not too worried.

https://codereview.chromium.org/1245013005/diff/40001/test/codegen/expect/syn...
File test/codegen/expect/syncstar_yield_test.txt (right):

https://codereview.chromium.org/1245013005/diff/40001/test/codegen/expect/syn...
test/codegen/expect/syncstar_yield_test.txt:2: info: [DynamicCast] expected
(dynamic) will need runtime check to cast to type String
(test/codegen/expect.dart, line 97, col 51)
these messages were skipped before because we didn't recompile "expect.dart"
when we started the compilation for "syncstar_yield_test.dart". This is an
artifact of codegen_test running multiple BatchCompiler instances against the
same AnalysisContext (which it should stop doing--though for the moment it's
improving our test coverage of analysis server use case)

[vsm, 2015-07-21 20:11:50]

lgtm

[Jennifer Messerly, 2015-07-21 20:15:49]

On 2015/07/21 20:11:50, vsm wrote:
> lgtm

thank you :)

it looks like
https://github.com/dart-lang/sdk/commit/646c84762d14e2bb137f9adcc6eb0d3f03662f69
is good so far on http://build.chromium.org/p/client.dart/console, so we should
be able to publish a new analyzer soon & can land this.

[Jennifer Messerly, 2015-07-21 22:37:00]

Committed patchset #3 (id:40001) manually as
1c029d0902387059b16866c0c41489e7739ea89a (presubmit successful).