Add comment in Headers.idl
Add comment in Headers.idl

"We should support Headers.prototype[Symbol.iterator]."

BUG=373120

Review URL: https://codereview.chromium.org/353333002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@177202 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs