Revert of Revert of Move SecurityLevel into a class of its own (patchset #1 id:1...

Revert of Revert of Move SecurityLevel into a class of its own (patchset #1 id:1 of https://codereview.chromium.org/1135373003/)

Reason for revert:
Reland initial patch. There is a fix for SecurityLevelTest:

https://codereview.chromium.org/1135073003

Original issue's description:
> Revert of Move SecurityLevel into a class of its own (patchset #19 id:420001 of https://codereview.chromium.org/1123943002/)
>
> Reason for revert:
> Android Tests dbg bot is failing:
> http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20(dbg)
>
> Failure example: http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/27901
>
> Original issue's description:
> > Move SecurityLevel into a class of its own
> >
> > This CL moves |GetSecurityLevelForWebContents| and the |SecurityLevel|
> > enum into a class of their own: |ConnectionSecurityHelper| in
> > //chrome/browser/ssl (since it is applying Chrome-specific security
> > policy to determine the security level of a page).
> >
> > Later, we will use the new |ConnectionSecurityHelper| class to compute a
> > security level for a page to send to the DevTools Security
> > panel. Specifically, we need to be able to calculate the security level
> > for a given page, not just the WebContents for the active tab.
> >
> > BUG=484392
> >
> > Committed: https://crrev.com/ca7c0a3374c21ab10c821f4f3a890afc79182acf
> > Cr-Commit-Position: refs/heads/master@{#329591}
> >
> > Committed: https://crrev.com/f50c9b4834e151aa6b5538545a503614cb74f5f9
> > Cr-Commit-Position: refs/heads/master@{#329724}
>
> TBR=felt@chromium.org,pkasting@chromium.org,rsleevi@chromium.org,bauerb@chromium.org,sky@chromium.org,tedchoc@chromium.org,estark@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=484392
>
> Committed: https://crrev.com/39722bb693112be3d91c729246c0ade351e7e900
> Cr-Commit-Position: refs/heads/master@{#329827}

TBR=felt@chromium.org,pkasting@chromium.org,rsleevi@chromium.org,bauerb@chromium.org,sky@chromium.org,tedchoc@chromium.org,estark@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=484392

Review URL: https://codereview.chromium.org/1124383007

Cr-Commit-Position: refs/heads/master@{#329832}