Added NVALGRIND define [on by default]. Can be turned off on valgrind slaves ...

tools/buildbot/master.chromium/master.cfg

Index: tools/buildbot/master.chromium/master.cfg
===================================================================
--- tools/buildbot/master.chromium/master.cfg	(revision 26230)
+++ tools/buildbot/master.chromium/master.cfg	(working copy)
@@ -573,7 +573,9 @@
 f_sub_dbg_linux = m_sub_linux.SubmoduleFactory('sub-dbg-linux', target='Debug')
 
 # On linux valgrind bots, override a few build settings.
-linux_valgrind_gyp_defines = 'release_optimize=1 werror= release_extra_cflags="-g"'
+linux_valgrind_gyp_defines = ('release_valgrind_build=1 '
+                              'release_optimize=1 werror= '
+                              'release_extra_cflags="-g"')
 
 f_chromium_rel_linux_valgrind_ui = F_LINUX(
     'chromium-rel-linux-valgrind-ui', target='Release',
@@ -756,7 +758,8 @@
 
 # On Mac valgrind bots, override the optimizer settings so we don't inline too
 # much and make the stacks harder to figure out.
-mac_valgrind_gyp_defines = 'mac_release_optimization=1'
+mac_valgrind_gyp_defines = ('release_valgrind_build=1 '
+                            'mac_release_optimization=1')
 
 # TODO(tvl): it would be nice to better tweak what is built by this to speed
 # up the compile cycle times.