Move DFG::OSRExitCompiler methods into DFG::OSRExit [step 1].

[Mark Lam]

This will minimize the code diff and make it easier to review the patch for https://bugs.webkit.org/show_bug.cgi?id=175144 later.  We'll do this patch in 3 steps:
1. Do the code changes to move methods into OSRExit.
2. Unify the 32-bit and 64-bit implementations of compileExit().
3. A follow up patch to actually copy the methods into DFGOSRExit.cpp, and delete the DFGOSRExitCompiler files.

Splitting this refactoring into these 3 steps also makes it easier to review this patch and understand what is being changed.

[Mark Lam]

Created attachment 317289 [details]
proposed patch.

[Mark Lam]

(In reply to Mark Lam from comment #0)
> 1. Do the code changes to move methods into OSRExit.
> 2. Unify the 32-bit and 64-bit implementations of compileExit().
> 3. A follow up patch to actually copy the methods into DFGOSRExit.cpp, and
> delete the DFGOSRExitCompiler files.

Let's change that.  I'll do this in the following steps instead:
1. Do the code changes to move methods into OSRExit.
2. Copy the 64-bit and common methods into DFGOSRExit.cpp, and delete the unused DFGOSRExitCompiler files.
3. Merge the 32-bit OSRExitCompiler methods into the 64-bit version, and delete DFGOSRExitCompiler32_64.cpp.

I think it's easier (and less error prone) to execute the refactoring this way.

[Radar WebKit Bug Importer]

<rdar://problem/33732402>

[Mark Lam]

Created attachment 317292 [details]
proposed patch.

[Saam Barati]

Comment on attachment 317292 [details]
proposed patch.

r=me

[Mark Lam]

Thanks for the review.  Landed in r220298: <http://trac.webkit.org/r220298>.