Cleanup of deoptimization environment copying functions.

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 644cb99c8471c14976986bf7cbdfda90c3ed077d..9dc34e7608a159cced31e423bc21ccc9570e7ff3 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -6701,10 +6701,10 @@ class Environment : public ZoneAllocated {
         function_(function),
         outer_(outer) { }
 
-  // Deep copy the environment.  A 'length' parameter can be given, which
-  // may be less than the environment's length in order to drop values
-  // (e.g., passed arguments) from the copy.
-  Environment* DeepCopy() const;
+  // Deep copy an environment.  A 'length' parameter can be given, which may
+  // be less than the environment's length in order to drop values (e.g.,
+  // passed arguments) from the copy.
+  Environment* DeepCopy() const { return DeepCopy(Length()); }
   Environment* DeepCopy(intptr_t length) const;
 
   GrowableArray<Value*> values_;