https://bugs.webkit.org/show_bug.cgi?id=32993

Reviewed by Dmitry Titov.

Add ENABLE_BLOB_SLICE feature define.

* configure.ac:

JavaScriptCore: Blob.slice support.
https://bugs.webkit.org/show_bug.cgi?id=32993

Reviewed by Dmitry Titov.

Add ENABLE_BLOB_SLICE feature define.
Also fix a problem that JSValue.toInteger is not exposed on Windows.

* Configurations/FeatureDefines.xcconfig:
* JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCore.def:

WebCore: Blob.slice support.
https://bugs.webkit.org/show_bug.cgi?id=32993

Reviewed by Dmitry Titov.

The following semantic is adopted per the discussions on public-webapps:
1) File.slice() does a synchronous IO to capture the current size and
   modification time and cache them in the resulting Blob.
2) Subsequent Blob operations, like Blob.slice and Blob.size simply
   use the cached values.
3) When the underlying file data are accessed, like in XHR.send(), the
   UA will check the cached modification time against the current
   modificat...