Native context: debug.js does not load from js builtins object anymore.

Native context: debug.js does not load from js builtins object anymore.

This mainly changes how we share ToBoolean, ToNumber and ToString between
native scripts. Instead of putting them on the js builtins object, we now
explicitly export and import those functions.

I also had to change the import/export mechanism slightly. Previously,
exports and imports are hooked up after all native scripts have been
executed. This means that imported functions cannot be called at the time
the native script is executed.

However, since ToBoolean (and also e.g. ObjectDefineProperties) is called
in v8natives.js, I changed the mechanism so that exports from previous
native scripts (runtime.js for ToBoolean) is imported immediately and can
be called.

R=cbruni@chromium.org

Committed: https://crrev.com/eb8c092822c7745b49d3d97ec93edc2b0af72827
Cr-Commit-Position: refs/heads/master@{#30244}

[Camillo Bruni, 2015-08-19 06:20:41]

lgtm

[Yang, 2015-08-19 07:20:35]

The CQ bit was checked by yangguo@chromium.org

[Yang, 2015-08-19 07:20:36]

The patchset sent to the CQ was uploaded after l-g-t-m from cbruni@chromium.org
Link to the patchset: https://codereview.chromium.org/1302533002/#ps20001
(title: "make importing requirement more explicit")

[commit-bot: I haz the power, 2015-08-19 07:20:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1302533002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1302533002/20001

[commit-bot: I haz the power, 2015-08-19 08:34:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-08-19 08:34:44]

Patchset 2 (id:??) landed as
https://crrev.com/eb8c092822c7745b49d3d97ec93edc2b0af72827
Cr-Commit-Position: refs/heads/master@{#30244}