This change introduces two new side-by-side channels for Google Chrome.
Chrome Beta can be installed via the --chrome-beta installer command
line switch, while Chrome Dev can be installed via the --chrome-dev
switch. Such installs have the following qualities:

- They install in ...\Google\Chrome (Beta,Dev)\Application (both
  per-machine and per-user installs are supported).
- They store their User Data directories in %LOCALAPPDATA%\Google\Chrome
  (Beta,Dev)\User Data.
- They register with Google Update under distinct appguids:
  - Beta: {8237E44A-0054-442C-B6B6-EA0509993955}
  - Dev : {401C381F-E0DE-4B85-8BD8-3F3F14FBDA57}
- Their shortcuts, taskbar, and Start Menu icons are badged with "Beta"
  or "Dev", as appropriate.
- While they will not prompt the user to be made the user's default
  browser, they support being made such via the usual platform UX flows.
- They self self-report as being on the "beta" and "dev" channels in
  user metrics and crash reporting, respectively.

BUG=373987
TEST=The test_installer build step covers general "will it blend"
tests. Manual testing should verify such things as:
- Does chrome://version show that the Executable and Profile paths
  contain "Beta" or "Dev"?
- Does chrome://version show "beta" or "dev" as the channel?
- Do the shortcut and taskbar icons thave the proper badge?
- Can these variations be installed alongside normal "Google Chrome"
  with no interference?

Review-Url: https://codereview.chromium.org/2802713002
Cr-Original-Commit-Position: refs/heads/master@{#466436}
Committed: https://chromium.googlesource.com/chromium/src/+/9897be5cb7fc7de9460c61e94eca2c4e27d99d8d
Review-Url: https://codereview.chromium.org/2802713002
Cr-Commit-Position: refs/heads/master@{#466560}