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In a previous attempt to prevent SadTab pages from being zoomable we
attempted to use RenderProcessHost::HasConnection, but this fails in
the case where a new tab can be started in the same RenderProcessHost
while the SadTab is still visible. This CL switches to testing to see
if the RenderView for the tab in question is live in order to avoid
this problem.

BUG=407562

Review URL: https://codereview.chromium.org/529993002

Cr-Commit-Position: refs/heads/master@{#292988}