Exclude TCMalloc tests when running under Valgrind.

These tests are not likely to ever work as Valgrind is already wrapping
malloc/free and thus changing the allocator behavior. Disabling these
tests for now and have filed crbug.com/567315 to track a long-term
decision about what to do with these tests.

BUG=567315
TBR=ssid@chromium.org

Review URL: https://codereview.chromium.org/1503233002

Cr-Commit-Position: refs/heads/master@{#363597}

tools/valgrind/gtest_exclude/base_unittests.gtest.txt

@@ -27,3 +27,7 @@ PlatformFile.TouchGetInfoPlatformFile
 
 # Crashes under Valgrind, see http://crbug.com/355436
 OutOfMemoryHandledTest.Unchecked*
+
+# Running under Valgrind breaks TCMalloc tests, see https://crbug.com/567315
+TCMallocTest.*
+TCMallocFreeTest.*