[ast] Mark temporaries as maybe-assigned by default.

src/ast/scopes.h

Index: src/ast/scopes.h
diff --git a/src/ast/scopes.h b/src/ast/scopes.h
index 1947a266c1637d162595d4297d066b8ae42bd24e..8a9422b67086f2a1209e4e3acadc6c569902a913 100644
--- a/src/ast/scopes.h
+++ b/src/ast/scopes.h
@@ -210,8 +210,10 @@ class V8_EXPORT_PRIVATE Scope : public NON_EXPORTED_BASE(ZoneObject) {
   // In particular, the only way to get hold of the temporary is by keeping the
   // Variable* around.  The name should not clash with a legitimate variable
   // names.
+  // Only pass kNotAssigned if you know what you are doing.

[adamk, 2017/02/15 19:03:59]

Not sure this comment is helpful. If this is dangerous enough, should the
version that takes a maybe_assigned argument be private?

   // TODO(verwaest): Move to DeclarationScope?
-  Variable* NewTemporary(const AstRawString* name);
+  Variable* NewTemporary(const AstRawString* name,
+                         MaybeAssignedFlag maybe_assigned = kMaybeAssigned);
 
   // ---------------------------------------------------------------------------
   // Illegal redeclaration support.