[clang-tidy] Apply modernize-use-auto in /content/renderer

This change applies clang-tidy's modernize-use-auto [1] in /content/renderer.
This change does not rewrite new and cast expressions.

Reproduction steps:
- run clang-tidy's modernize-use-auto
- run git cl format
- manually remove unused typedefs due to -Wunused-local-typedef error

[1] https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-auto.html

This CL was uploaded by git cl split.

[email protected]

Bug: 890902
Change-Id: I50debb7aaf123e76bb03925e7720ab5be5dd16a8
Reviewed-on: https://chromium-review.googlesource.com/c/1257906
Reviewed-by: Kentaro Hara <[email protected]>
Commit-Queue: Jan Wilken Dörrie <[email protected]>
Cr-Commit-Position: refs/heads/master@{#596050}
43 files changed