Use placement-new for zone-allocation in the Lithium classes.

This avoid calling Isolate::Current on each zone-allocation of
a Lithium object.
Review URL: http://codereview.chromium.org/8429001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9856 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/lithium-ia32.h

@@ -2166,6 +2166,7 @@ class LChunkBuilder BASE_EMBEDDED {
       : chunk_(NULL),
         info_(info),
         graph_(graph),
+        isolate_(graph->isolate()),
         status_(UNUSED),
         current_instruction_(NULL),
         current_block_(NULL),
@@ -2195,6 +2196,7 @@ class LChunkBuilder BASE_EMBEDDED {
   LChunk* chunk() const { return chunk_; }
   CompilationInfo* info() const { return info_; }
   HGraph* graph() const { return graph_; }
+  Zone* zone() { return isolate_->zone(); }
 
   bool is_unused() const { return status_ == UNUSED; }
   bool is_building() const { return status_ == BUILDING; }
@@ -2306,6 +2308,7 @@ class LChunkBuilder BASE_EMBEDDED {
   LChunk* chunk_;
   CompilationInfo* info_;
   HGraph* const graph_;
+  Isolate* isolate_;
   Status status_;
   HInstruction* current_instruction_;
   HBasicBlock* current_block_;