Reduce flakes in the mini_installer test.

Reduce flakes in the mini_installer test.

This change makes the test more resilient to unexpected state on the
machine.

- RegistryVerifier can now verify that registry values are not present
  (and, as a result, optional registry keys). A key's "exists" property
  can be one of "required", "forbidden", or "optional". The first two
  behave identically to the true and false boolean values of the
  previous implementation. For an "optional" key, values within it may
  have an empty dict (i.e., with no "type" or "data" members) to
  indicate that the value must not be present in the key if the key is
  present.

- Each test now begins with the "no_pv" state rather than the "clean"
  state. This is more permissive, and simply ensures that Chrome is not
  registered with Google Update.

- After attempting to force-uninstall Chrome (either before executing a
  test or after a test failure), the harness will unconditionally delete
  the Google Update registration of that Chrome if it is present. This
  will clean the machine sufficiently for a subsequent test run.

BUG=375739, 401148, 402081
R=robertshield@chromium.org
NOTRY=true

Committed: https://crrev.com/92a819b0b7898057df793b90d66ca0d31c4d9063
Cr-Commit-Position: refs/heads/master@{#292943}

[robertshield, 2014-09-02 15:45:27]

lgtm

https://codereview.chromium.org/520633005/diff/20001/chrome/test/mini_install...
File chrome/test/mini_installer/registry_verifier.py (right):

https://codereview.chromium.org/520633005/diff/20001/chrome/test/mini_install...
chrome/test/mini_installer/registry_verifier.py:75: # Values are not checked if
the missing key's existence is optional.
Can you reference this in the method comment?

[grt (UTC plus 2), 2014-09-02 16:37:11]

Thanks!

https://codereview.chromium.org/520633005/diff/20001/chrome/test/mini_install...
File chrome/test/mini_installer/registry_verifier.py (right):

https://codereview.chromium.org/520633005/diff/20001/chrome/test/mini_install...
chrome/test/mini_installer/registry_verifier.py:75: # Values are not checked if
the missing key's existence is optional.
On 2014/09/02 15:45:27, robertshield wrote:
> Can you reference this in the method comment?

Done.

[grt (UTC plus 2), 2014-09-02 16:37:15]

The CQ bit was checked by grt@chromium.org

[commit-bot: I haz the power, 2014-09-02 16:38:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/grt@chromium.org/520633005/40001

[commit-bot: I haz the power, 2014-09-02 16:39:47]

Committed patchset #2 (id:40001) as 6bd93bb9b248a64398f1a5d10758ea12fd96b9df

[commit-bot: I haz the power, 2014-09-10 03:19:00]

Patchset 2 (id:??) landed as
https://crrev.com/92a819b0b7898057df793b90d66ca0d31c4d9063
Cr-Commit-Position: refs/heads/master@{#292943}