Optimize functions containing try-catch.

runtime/vm/scopes.h

Index: runtime/vm/scopes.h
===================================================================
--- runtime/vm/scopes.h	(revision 22436)
+++ runtime/vm/scopes.h	(working copy)
@@ -32,6 +32,7 @@
       is_final_(false),
       is_captured_(false),
       is_invisible_(false),
+      always_live_(false),
       index_(LocalVariable::kUnitializedIndex) {
     ASSERT(type.IsZoneHandle());
     ASSERT(type.IsFinalized());
@@ -72,6 +73,9 @@
     is_invisible_ = value;
   }
 
+  bool always_live() const { return always_live_; }
+  void mark_as_always_live() { always_live_ = true; }
+
   bool IsConst() const {
     return const_value_ != NULL;
   }
@@ -109,6 +113,7 @@
   bool is_captured_;  // If true, this variable lives in the context, otherwise
                       // in the stack frame.
   bool is_invisible_;
+  bool always_live_;
   int index_;  // Allocation index in words relative to frame pointer (if not
                // captured), or relative to the context pointer (if captured).