Revert of Fix crash when user closes window prior to the "Confirm Install" prompt showing (patchset #9 id:270001 of https://codereview.chromium.org/662073002/)

Reason for revert:
Broke test on the GPU waterfall http://build.chromium.org/p/chromium.gpu/builders/GPU%20Mac%20Builder%20%28dbg%29/builds/20292/steps/compile/logs/stdio

Original issue's description:
> Fix crash when user closes window prior to the "Confirm Install" prompt showing.
>
> This CL moves ExtensionInstallPrompt::ShowParams to its own class. The new class
> observes the content::WebContents and gfx::NativeWindow for their destruction.
>
> If the window is closed prior to the "Confirm Install" prompt showing, the
> prompt is shown as a non-modal free-standing dialog.
>
> BUG=422814
> TEST=ExtensionInstallPromptBrowserTest.*
>
> Committed: https://crrev.com/d53564d3743bc2da768b38f0db34090a7bb43fea
> Cr-Commit-Position: refs/heads/master@{#301674}

TBR=asargent@chromium.org,sky@chromium.org,thakis@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=422814

Review URL: https://codereview.chromium.org/683993002

Cr-Commit-Position: refs/heads/master@{#301702}
26 files changed