[debugger] expose side-effect free evaluate to inspector.

src/debug/mirrors.js

Index: src/debug/mirrors.js
diff --git a/src/debug/mirrors.js b/src/debug/mirrors.js
index 94e45dff8299d27b5aec57937d42c4d328719e95..cbf15ef623ceac5e817ec4d68d32a48285fa58de 100644
--- a/src/debug/mirrors.js
+++ b/src/debug/mirrors.js
@@ -1919,11 +1919,12 @@ FrameMirror.prototype.allScopes = function(opt_ignore_nested_scopes) {
 };
 
 
-FrameMirror.prototype.evaluate = function(source) {
+FrameMirror.prototype.evaluate = function(source, allow_side_effect = true) {
   return MakeMirror(%DebugEvaluate(this.break_id_,
                                    this.details_.frameId(),
                                    this.details_.inlinedFrameIndex(),
-                                   source));
+                                   source,
+                                   allow_side_effect));
 };