Invoke LeakSanitizer on teardown of some browser test fixtures.

Call LeakSanitizer before RenderViewTest::TearDown(), as the latter may leak
WebKit objects when it shuts down V8. This call really belongs in
RenderViewTest::TearDown(), but unfortunately there are unit tests which inherit
from RenderViewTest, whereas this approach is only suitable for browser tests.
Anyway this is intended as a temporary fix, as Oilpan is expected to rid us of
those leaks.

BUG=328552
TBR=phajdan.jr@chromium.org, fsamuel@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/187473004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255016 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255016