Enable TCMalloc on Linux by default.

tools/valgrind/memcheck/suppressions.txt

Index: tools/valgrind/memcheck/suppressions.txt
diff --git a/tools/valgrind/memcheck/suppressions.txt b/tools/valgrind/memcheck/suppressions.txt
index 3178cf1f63fe5e3ba420670b1827b4438a300708..3f1f6541bd35507d856a39d33c686ba43e8b96cf 100644
--- a/tools/valgrind/memcheck/suppressions.txt
+++ b/tools/valgrind/memcheck/suppressions.txt
@@ -346,6 +346,32 @@
    ...
    obj:/bin/ps
 }
+{
+   # Valgrind issues with tcmalloc's VDSOSupport module
+   bug_28149a
+   Memcheck:Addr1
+   fun:_ZN4base11VDSOSupport11ElfMemImage4InitEPKv
+   fun:_ZN4base11VDSOSupport11ElfMemImageC1EPKv
+   fun:_ZN4base11VDSOSupportC1Ev
+   fun:_ZN4base11VDSOSupport4InitEv
+   fun:_ZN4base14VDSOInitHelperC1Ev
+   fun:_Z41__static_initialization_and_destruction_0ii
+   fun:_GLOBAL__I__ZN4base11VDSOSupport12kInvalidBaseE
+   obj:/b/slave/webkit-rel-linux-valgrind-layout/build/src/sconsbuild/Release/test_shell
+   obj:/b/slave/webkit-rel-linux-valgrind-layout/build/src/sconsbuild/Release/test_shell
+   fun:__libc_csu_init
+   fun:(below main)
+}
+{
+   # Valgrind issues with tcmalloc's VDSOSupport module
+   bug_28149b
+   Memcheck:Addr4
+   ...
+   fun:_ZNK4base11VDSOSupport12LookupSymbolEPKcS2_iPNS0_10SymbolInfoE
+   ...
+   fun:_Z41__static_initialization_and_destruction_0ii
+   ...
+}
 
 #-----------------------------------------------------------------------
 # 2. intentional unit test errors, or stuff that is somehow a false positive