Create a ModuleSystem even for blank pages

We assumed that a v8::Context associated with a frame that were pointing
to "about:blank" was never reused when visiting other URL. This
assumption is incorrect, there are situations (like the cases triggered
by the bugs linked) that the v8::Context is reused to the page loaded.

Since the frame URL can change from "about:blank" to something else
between the calls DidCreateScriptContext() and
WillReleaseScriptContext(), we can't rely on that information. The crash
was caused by assuming that if the URL wasn't blank at
WillReleaseScriptContext() time, we had a module.

The intent of not creating module system for blank pages was to avoid
unnecessary work. This will be accomplished in the future by other means
like avoiding to load the JavaScript code that's not used.

Fixes #626 and #602.
Change ContextDestruction test to be less picky about titles

For the test move forward, we depended on the exact sequence of
instances being created. We can cover the same behavior (which is
instances will be created and not reused), without having to indicate
this in the title.

This allows us to be be lax about the exact number of instances created
now, until we add support for loading instances on demand ("lazy loading
of instances").
Automated test for issue 602

This adds a reduction of the problem identified in
https://github.com/crosswalk-project/crosswalk/issues/602 to our
browsertests. In summary: we should not crash when an empty iframe have
document.write() called for it. See comments in the added test for
details.
Merge pull request #632 from cmarcelo/blank-page-fix

Always create module systems