Remove all functionality from class HSubgraph.

Remove all functionality from class HSubgraph.

Move the member functions of HSubgraph to HGraphBuilder.

Committed: http://code.google.com/p/v8/source/detail?r=6958

[Kevin Millikin (Chromium), 2011-02-23 16:49:17]

All the AppendXXX functions on HSubgraph moved to HGraphBuilder.  I elected to
name them CreateXXX (they're not appending anymore, and BuildXXX is used for
macros that generate chunks of instructions, these glue together bits of graph),
and to have them return the distinguished exit block of the thing they create.

Next is to get rid of Create...Subgraph and AddToSubgraph.

[fschneider, 2011-02-24 13:09:44]

LGTM.

http://codereview.chromium.org/6573006/diff/1/src/hydrogen.cc
File src/hydrogen.cc (right):

http://codereview.chromium.org/6573006/diff/1/src/hydrogen.cc#newcode552
src/hydrogen.cc:552: } else {
here you could write 

} else if (...) {

}

[Kevin Millikin (Chromium), 2011-02-28 08:53:29]

http://codereview.chromium.org/6573006/diff/1/src/hydrogen.cc
File src/hydrogen.cc (right):

http://codereview.chromium.org/6573006/diff/1/src/hydrogen.cc#newcode552
src/hydrogen.cc:552: } else {
On 2011/02/24 13:09:44, fschneider wrote:
> here you could write 
> 
> } else if (...) {
> 
> }

Good catch.  I'll hold off for now because the "if (blah != NULL)
blah->Goto(whocares);" seems like an idiom that we might abstract, so I'd like
to keep it exactly that way in the code.