Fix build - create output dir if needed

Fix build - create output dir if needed

TBR=jmesserly@google.com

Committed: https://github.com/dart-lang/dev_compiler/commit/ed47365eaa6985199555289616b242d2c2878a43

[vsm, 2015-10-02 21:23:46]

Committed patchset #1 (id:1) manually as
ed47365eaa6985199555289616b242d2c2878a43 (presubmit successful).

[Jennifer Messerly, 2015-10-03 00:23:02]

https://codereview.chromium.org/1378763006/diff/1/test/codegen_test.dart
File test/codegen_test.dart (right):

https://codereview.chromium.org/1378763006/diff/1/test/codegen_test.dart#newc...
test/codegen_test.dart:137: if (!outDir.existsSync())
outDir.createSync(recursive: true);
hmm, shouldn't this line do what we need?

ideally we could consolidate these checks. Maybe it's the compiler's
responsibility to create the output directory.

[vsm, 2015-10-05 17:40:47]

On 2015/10/03 00:23:02, John Messerly wrote:
> https://codereview.chromium.org/1378763006/diff/1/test/codegen_test.dart
> File test/codegen_test.dart (right):
> 
>
https://codereview.chromium.org/1378763006/diff/1/test/codegen_test.dart#newc...
> test/codegen_test.dart:137: if (!outDir.existsSync())
> outDir.createSync(recursive: true);
> hmm, shouldn't this line do what we need?
> 
> ideally we could consolidate these checks. Maybe it's the compiler's
> responsibility to create the output directory.

The txt file was sometimes one level down from the outDir.  If we didn't also
generate JS due to static error, the compiler didn't create the dir.

Perhaps the compiler should be responsible for creating the error file (txt or
whatever format) as well - probably cleaner than the current callback into
codegen_text.

[Jennifer Messerly, 2015-10-05 17:44:57]

lgtm then, yeah, hopefully we can sort this out into something cleaner