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Tests in the interative_ui_tests fixture are known to timeout if there's
an always-on-top window on the desktop. This change introduces a few
improvements to the existing data collection strategy to help diagnose
the provenance of these always-on-top windows.

- Checks for always-on-top windows are moved out of the test child
  processes and up to the parent test proc. This is a more reliable
  place to log any info, as such log messages are more likely to make it
  into the main swarming log output. This is a result of the way
  GetTestOutputSnippet pulls what it thinks is the only relevant test
  output -- it drops messages emitted outside of the test body.

- Scans for always-on-top windows now take place before running any test
  in the shard and after any test that times out.

- A screen snapshot is saved if any always-on-top window is found, even
  in the case of dialogs that will be closed.

- An attempt is made to find and emit the command lines for all
  processes in the process hierarchy of the proc owning an always-on-top
  window.

- All details are emitted in a single log message. For example:

There is an always on top window on the desktop after this test timed out. This may have been caused by this test or a previous test and may cause flakes; window class name: ConsoleWindowClass; subprocess command line: "".\interactive_ui_tests.exe" --brave-new-test-launcher --cfi-diag=0 --gtest_also_run_disabled_tests --gtest_filter=AutofillInteractiveTest.AutofillViaClick --single_process --snapshot-output-dir="e:\b\s\w\iomhwbd8" --test-launcher-bot-mode --test-launcher-output="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir6396_16240\results6396_26680\test_results.xml" --test-launcher-summary-output="e:\b\s\w\iomhwbd8\output.json" --user-data-dir="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir6396_16240\d6396_27306""; owning process lineage: (process_id: 2000, command_line: "C:\Windows\system32\cmd.exe /c ""C:\Users\chrome-bot\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\run_swarm_bot.bat" ""), (process_id: 1496, command_line: "C:\Windows\Explorer.EXE"); screen snapshot saved to file: "e:\b\s\w\iomhwbd8\ss_20171030114011_636.png";

BUG=764415
R=sky@chromium.org

Change-Id: I1aed3a41542680b197c7856e1f5d9ec9af6e3774
Reviewed-on: https://chromium-review.googlesource.com/737641Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513095}