Refactor Hydrogen environment liveness analysis into an HPhase.

src/hydrogen-environment-liveness.h

Index: src/hydrogen-environment-liveness.h
diff --git a/src/hydrogen-environment-liveness.h b/src/hydrogen-environment-liveness.h
index 484e56d52eb0d54f31106a8439baa285dd6a763d..3ad91bdec795e4afdde955dbd24b747d31d53aa7 100644
--- a/src/hydrogen-environment-liveness.h
+++ b/src/hydrogen-environment-liveness.h
@@ -45,9 +45,9 @@ namespace internal {
 // HOptimizedGraphBuilder::IsEligibleForEnvironmentLivenessAnalysis().
 class EnvironmentSlotLivenessAnalyzer {
  public:
-  explicit EnvironmentSlotLivenessAnalyzer(HGraph* graph);
+  EnvironmentSlotLivenessAnalyzer(HGraph* graph, Zone* phase_zone);
 
-  void AnalyzeAndTrim();
+  void Run();
 
  private:
   void ZapEnvironmentSlot(int index, HSimulate* simulate);
@@ -56,13 +56,11 @@ class EnvironmentSlotLivenessAnalyzer {
   void UpdateLivenessAtBlockEnd(HBasicBlock* block, BitVector* live);
   void UpdateLivenessAtInstruction(HInstruction* instr, BitVector* live);
 
-  Zone* zone() { return &zone_; }
+  Zone* phase_zone() { return phase_zone_; }
 
   HGraph* graph_;
-  // Use a dedicated Zone for this phase, with a ZoneScope to ensure it
-  // gets freed.
-  Zone zone_;
-  ZoneScope zone_scope_;
+  Zone* phase_zone_;
+  ZoneScope phase_zone_scope_;
 
   int block_count_;