policy: generate JSON schema at build time as a string constant.

policy: generate JSON schema at build time as a string constant.

This is CL 1 of 3 that loads policy on Windows using the schema.

The policy generator now creates a constant kPolicyJsonSchema in
policy_constants.h that defines the expected structure of Chrome
policy data.  This schema is generated from the existing policy
templates file.

BUG=270667

[Joao da Silva, 2013-09-11 11:43:37]

Looks good.

Please add a unittest at //chrome/browser/policy verifying that
PolicySchema::Parse successfully parses policy::kPolicyJsonSchema. The test can
additionally verify that a couple of policies have the expected schema (e.g.
some boolean policy, a string policy, an interger, a string list, and maybe
ProxySettings). This will catch regressions and invalid schemas added to the
template.

Also, the string generated on Linux is 16KB, which is a bit large. Including
only supported policies may halve this, but we should consider other options to
reduce this if it gets larger. Maybe leave a TODO and a bug for this.

https://codereview.chromium.org/22364011/diff/18001/chrome/tools/build/genera...
File chrome/tools/build/generate_policy_source.py (right):

https://codereview.chromium.org/22364011/diff/18001/chrome/tools/build/genera...
chrome/tools/build/generate_policy_source.py:19: import json
alread in line 14

https://codereview.chromium.org/22364011/diff/18001/chrome/tools/build/genera...
chrome/tools/build/generate_policy_source.py:322:
schema['properties'][policy.name] = policy.schema
make this conditional on policy.is_supported.

[Joao da Silva, 2013-09-11 11:59:00]

https://codereview.chromium.org/22364011/diff/18001/chrome/tools/build/genera...
File chrome/tools/build/generate_policy_source.py (right):

https://codereview.chromium.org/22364011/diff/18001/chrome/tools/build/genera...
chrome/tools/build/generate_policy_source.py:324:
json.dumps(json.dumps(schema)))
pass separators=(',', ':') to these 2 calls. It will remove the whitespaces
after commas and colons, and save some more bytes.