Add script streaming API.

Add script streaming API.

Blink will use this API to stream script data into V8 as the scripts
load. During loading, V8 can already parse the scripts. They will be then
compiled and executed when the loading is complete.

This is a reincarnation of https://codereview.chromium.org/366153002/
with fixes.

BUG=
R=jochen@chromium.org, rossberg@chromium.org, svenpanne@chromium.org, yangguo@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=23904

[marja, 2014-09-11 12:04:34]

FYI, here's the fixed version of the streaming API cl. Patch set 1 is the
original version and patch set 2 is the fixed version.

[jochen (gone - plz use gerrit), 2014-09-11 12:05:00]

lgtm assuming tryjobs are happy :)

[marja, 2014-09-11 14:32:24]

Patchset #3 (id:40001) has been deleted

[marja, 2014-09-12 08:43:42]

Offline discussion with jochen@ and svenpanne@ about the size_t fix:

- The correct type for the GetMoreData return value is size_t
- Unfortunately, V8 uses unsigned internally
- Decided to static_cast it + a TODO to make the internal types correct
- Practically, Blink is not going to pass data lengths which are bigger than
unsigned can hold (SharedBuffer on the Blink side uses unsigned, too).

[marja, 2014-09-12 09:12:25]

Committed patchset #7 (id:140001) manually as 23904 (presubmit successful).