Revert of Background tracing: Tracing scenarios can now enable/disable Blink features, for A/B testing purpos…

Revert of Background tracing: Tracing scenarios can now enable/disable Blink features, for A/B testing purpos… (patchset #2 id:20001 of https://codereview.chromium.org/1420033003/ )

Reason for revert:
Revert due to:

content_browsertests failure:
BackgroundTracingManagerBrowserTest.SetActiveScenarioFailsWithInvalidPreemptiveConfig

content_unittests failures:
BackgroundTracingConfigTest.PreemptiveConfigFromInvalidString
BackgroundTracingConfigTest.ReactiveConfigFromInvalidString

Build link:
https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/48840

Original issue's description:
> Background tracing: Tracing scenarios can now enable/disable Blink features, for A/B testing purposes.
>
> Also added a scenario name to the config, for easier filtering on the backend.
>
> R=dsinclair,shatch
> BUG=546193
>
> Committed: https://crrev.com/1607e4b8ae91d4c9ab09c54405c468e989b96e9b
> Cr-Commit-Position: refs/heads/master@{#356101}

TBR=dsinclair@chromium.org,simonhatch@chromium.org,fmeawad@chromium.org,oysteine@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=546193
Committed: https://crrev.com/23da63b66d8fb03f521e136b4f4ea9b13945d34c
Cr-Commit-Position: refs/heads/master@{#356132}

[dcaiafa, 2015-10-26 21:45:11]

Created Revert of Background tracing: Tracing scenarios can now enable/disable
Blink features, for A/B testing purpos…