Fix cctest/test-types.cc to gcc 4.7's name lookup changes.

Fix cctest/test-types.cc to gcc 4.7's name lookup changes.

In GCC 4.7 the name lookup method is changed:
"The C++ compiler no longer performs some extra unqualified lookups it had performed in the past, namely dependent base class scope lookups and unqualified template function lookups."

BUG=
TEST=cctest/test-types

[kilvadyb, 2014-01-22 13:23:18]

We got the following compilation errors using gcc 4.7:
../test/cctest/test-types.cc: In instantiation of 'void Tests<Type, TypeHandle,
Region, Rep>::Union() [with Type =
v8::internal::TypeImpl<v8::internal::ZoneTypeConfig>; TypeHandle =
v8::internal::TypeImpl<v8::internal::ZoneTypeConfig>*; Region =
v8::internal::Zone; Rep = ZoneRep]':
../test/cctest/test-types.cc:803:21:   required from here
../test/cctest/test-types.cc:433:5: error: 'IsBitset' was not declared in this
scope, and no declarations were found by argument-dependent lookup at the point
of instantiation [-fpermissive]
../test/cctest/test-types.cc:433:5: note: declarations in dependent base
'ZoneRep' are not found by unqualified lookup
../test/cctest/test-types.cc:433:5: note: use 'this->IsBitset' instead

 Following the suggestion of gcc4.7, this-> solves the problem.

[kisg, 2014-01-22 13:54:39]

LGTM, but we need additional approval for this.

Jakob, Benedikt: Could you please take a look?

[danno, 2014-01-22 15:37:49]

lgtm

[Paul Lind, 2014-01-22 17:50:12]

This fix is now a duplicate of https://codereview.chromium.org/134643025, which
landed as 18756. So this can be closed.