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- Update chrome_app manifest to support 32 and 192px icons.
- Use 192px icon as window icon for Chrome browser.
- Move all resource handing related to chrome_app under
  OS_CHROMEOS ifdef.

Bug: 879618
Test: manual
Change-Id: If3e9fb396424159ea0bf7f2cf61febfd89838b62
Reviewed-on: https://chromium-review.googlesource.com/1210943
Commit-Queue: Vladislav Kaznacheev <kaznacheev@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589771}