Disable ScreenCaptureDeviceTest.Capture under Valgrind on Mac

BUG=244102
NOTRY=true
R=timurrrr@chromium.org

ScreenCaptureDeviceTest.Capture causes SEGV_MAPERR under Mac Valgrind. Bug
244102.

Review URL: https://chromiumcodereview.appspot.com/16104003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202417 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/gtest_exclude/media_unittests.gtest_mac.txt

+# Crashes due to memory errors, probably in WebRTC, see http://crbug.com/244102
+ScreenCaptureDeviceTest.Capture