Revert of Debugger: use FrameInspector in ScopeIterator to find context. (patchset #3 id:40001 of https://codereview.chromium.org/1239033002/)

Reason for revert:
breaks roll: http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/87292/steps/browser_tests%20%28with%20patch%29/logs/DevToolsSanityTest.TestPauseWhenScriptIsRunning

Original issue's description:
> Debugger: use FrameInspector in ScopeIterator to find context.
>
> In optimized code, it's not guaranteed that the current context
> is stored in its frame slot.
>
> R=bmeurer@chromium.org
> BUG=v8:4309
> LOG=N
>
> Committed: https://crrev.com/3a0ee39cbde6a9778cfc4e2a6a0a8ff68933ff38
> Cr-Commit-Position: refs/heads/master@{#29697}

TBR=bmeurer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4309

Review URL: https://codereview.chromium.org/1243553002

Cr-Commit-Position: refs/heads/master@{#29722}