Preserve original Identifier node name somewhere: required for source-map names array

[nopnop]

The source-map names array of the Source Map Revision 3 Proposal, allows you to find the original name of a mangled identifier.

Introduced in escodegen: estools/escodegen#113, the resulting names array is wrong (the names used are the mangled names, not the originals names).

May I suggest to keep somewhere in the mangled node, a property with the original name (sourceName or whatever) ?

{ type: 'Identifier',
  name: 'a',
  sourceName: 'foobar',
  range: [ 362, 363 ],
  loc: 
   { start: { line: 15, column: 17 },
     end: { line: 15, column: 18 } } }

Then, this pr estools/escodegen#113 may be re-open to use sourceName instead of name.

[tarruda]

@nopnop does any browser currently supports this feature? For me chrome still shows the mangled variable names(when debugging with source maps, hovering over an original variable name does nothing)