Make only slow (Valgrind and DR) tools use the *.gtest.txt files 
Make only slow (Valgrind and DR) tools use the *.gtest.txt files 

As the number of our tools grows, it's correct no more to unconditionally append the contents of *.gtest.txt files to the gtest filters.
Currently such files contain specific filters common for Memcheck and TSan on Linux and Mac, and Dr.Memory on Windows, so I propose to use these filters only for those tools. 

In the future those can be renamed to *.gtest_slow.txt. 
Anyway, I doubt there should be global test filters used by all the tools.
Review URL: http://codereview.chromium.org/7926008

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@101848 0039d316-1c4b-4281-b951-d872f2087c98

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