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Creating 2 prototype tests using EG2 with the smoke_egtest suite.
The plan for migrating to EG2 is outlined at go/chrome-eg2-migration.

- Added the earl_grey2:all_tests as a build target
- Added the ios/chrome/test/earl_grey2 directory with BUILD and gni files
- Added the prototype smoke_test suite with 2 test cases
- Added the chrome_earl_grey_edo .h/mm files for the EDO helpers
- Tweaked and reorganized ios/third_party/earl_grey2/ BUILD and gni files.

Bug: 906201
Change-Id: I6521af6403ac9e4b320cba25f390be88522a0678
Reviewed-on: https://chromium-review.googlesource.com/c/1352532
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619732}