Teach bytecode liveness about the debugger

[Saam Barati]

Specifically, we should treat the scope as always live.
There is currently a bug where we tier up to the FTL, then throw an exception using 'throw'.
This causes us to OSR exit to baseline. The OSR exit believes the scope is dead. But it's not.
When debugging is enabled, it's always fair game to read from the scope register.

[Saam Barati]

This program crashes when run w/ debugging opcodes and shadow chicken:
```
"use strict";
function foo(b) {
    if (b)
        throw "foo";
    return b;
}
noInline(foo);


for (let i = 0; i < 10000; i++)
    foo(false);

foo(true);
```

[Saam Barati]

Created attachment 280295 [details]
patch

[Build Bot]

Comment on attachment 280295 [details]
patch

Attachment 280295 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.webkit.org/results/1420927

New failing tests:
inspector/debugger/call-frame-this-nonstrict.html

[Build Bot]

Created attachment 280298 [details]
Archive of layout-test-results from ews103 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews103  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 280295 [details]
patch

Attachment 280295 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.webkit.org/results/1420941

New failing tests:
inspector/debugger/call-frame-this-nonstrict.html

[Build Bot]

Created attachment 280300 [details]
Archive of layout-test-results from ews105 for mac-yosemite-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews105  Port: mac-yosemite-wk2  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 280295 [details]
patch

Attachment 280295 [details] did not pass mac-debug-ews (mac):
Output: http://webkit-queues.webkit.org/results/1420943

New failing tests:
inspector/debugger/call-frame-this-nonstrict.html

[Build Bot]

Created attachment 280301 [details]
Archive of layout-test-results from ews113 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews113  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[BJ Burg]

<rdar://problem/26571493>

[Saam Barati]

Created attachment 280351 [details]
patch

[WebKit Commit Bot]

Comment on attachment 280351 [details]
patch

Clearing flags on attachment: 280351

Committed r201622: <http://trac.webkit.org/changeset/201622>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.