System Clipboard: Use Range-based For Loops

- Using range-based for loops whenever possible in blink/renderer/core/clipboard/
- No logic changes.

Bug: 896479
Change-Id: I45a38eb0387227a54627fe329178cceec537c2d1
Reviewed-on: https://chromium-review.googlesource.com/c/1427793
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626687}
2 files changed