Remove shadowing variables in blink/platform

I'm interested in avoiding and possibly banning shadowed variables since I think that might
possibly prevent jumbo problems. This patch resolves all current issues of shadowed
variables in blink/platform, mostly through natural renamings or refactorings.

The exact warnings this patch avoids are a bit too many to list here but is available at
https://chromium-review.googlesource.com/c/chromium/src/+/1436042/11//COMMIT_MSG

Bug: 925310                                               ^

Change-Id: I9f94b4facb075db6b5860e9e942caddc1c51faee
Reviewed-on: https://chromium-review.googlesource.com/c/1436042
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633235}
13 files changed