Use zone when allocating handles in FlowGraphCompiler assembling operations. Add profiling VM tags…

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index c9436800f88e6818215170134db905fc7623ed6d..44919ffa9451c45b08ed18efcbd1acac46d62809 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -1748,7 +1748,7 @@ class Definition : public Instruction {
   //    - non-constant sentinel
   //    - a constant (any non-sentinel value)
   //    - unknown sentinel
-  Object& constant_value() const { return constant_value_; }
+  Object& constant_value();
 
   virtual void InferRange(RangeAnalysis* analysis, Range* range);
 
@@ -1801,7 +1801,7 @@ class Definition : public Instruction {
   Value* input_use_list_;
   Value* env_use_list_;
 
-  Object& constant_value_;
+  Object* constant_value_;
 
   DISALLOW_COPY_AND_ASSIGN(Definition);
 };