Session restore: Use the same TabLoader for all profiles.
Session restore: Use the same TabLoader for all profiles.

When several profiles are restored at the same time, this decreases
the number of tabs loading in parallel.

BUG=124235
TEST=NONE


Review URL: http://codereview.chromium.org/10122007

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@133411 0039d316-1c4b-4281-b951-d872f2087c98

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