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This CL weeds out more instances of raw new and replaces them with
std::make_unique<>, wherever appropriate, per this guideline:
https://chromium.googlesource.com/chromium/src/+/HEAD/styleguide/c++/c++-dos-and-donts.md#use-and-instead-of-bare

In one instance, there's no need of a pointer, so it's been removed.

Bug: 932591
Change-Id: I0b99d8ebc468bd7c496b7d50844f46fea2d68b44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529090Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641686}