UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:53.0) Gecko/20100101 Firefox/53.0

Steps to reproduce the problem:
1. Open attached poc.html in Chrome.
2. Open DevTools debugger.
3. Set breakpoints in lines 8, 14, and 18.
4. Reload to hit first breakpoint; resume twice to reach the others.

What is the expected behavior?
- Top-level variables bound with ES6 let/const (in poc.html: letGlobal/constGlobal) should be shown as "undefined" before reaching their declaration statements in the debugger.
- This would be consistent with let/const in blocks and functions.

What went wrong?
- Top-level variables bound with ES6 let/const are not shown in the debugger (under Scope) until the declaration statement is executed, see screenshot global-let-not-shown-png. Let/const-bound variables in function and block scopes are shown in the debugger as undefined, see block-let-undefined.png

Did this work before? N/A 

Chrome version: 58.0.3029.81 (Developer Build)  Channel: stable
OS Version: Ubuntu 16.10 (64-bit)
Flash Version: Shockwave Flash 25.0 r0

- The behavior of let/const bindings in function/block scopes, namely showing the variables as undefined in "Scope", is useful for developers. One can quickly see all bindings made in the function/block.
- It is also consistent with http://www.ecma-international.org/ecma-262/6.0/#sec-let-and-const-declarations: "let and const declarations define variables that are scoped to the running execution context’s LexicalEnvironment. The variables are created when their containing Lexical Environment is instantiated [...]"
- According to http://www.ecma-international.org/ecma-262/6.0/#sec-lexical-environments "A global environment is a Lexical Environment [...]", so I expected the debugger to behave the same for let/const in the global scope as in functions/blocks.
 

Deleted: poc.html 626 bytes

poc.html 626 bytes View Download

Deleted: block-let-undefined.png 73.6 KB

	block-let-undefined.png 73.6 KB View Download

Deleted: global-let-not-shown.png 70.5 KB

	global-let-not-shown.png 70.5 KB View Download