Revert 35189 (caused test_shell_tests crashes on valgrind bot):

Take 2: Reenable TCMalloc on Linux and make POSIX signal handling async signal safe.
Reinstates r34096 and r34036, which were reverted by r34632 due to hanging ui_tests and browser_tests on bots.
I've been unable to repro on the trybots despite hitting them with a ton of try jobs, so I'm trying on the buildbots again.
BUG=http://crbug.com/30501

Review URL: http://codereview.chromium.org/505068

TBR=willchan@chromium.org
Review URL: http://codereview.chromium.org/517001

git-svn-id: http://src.chromium.org/svn/trunk/src/build@35192 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -187,7 +187,7 @@
     'linux_strip_binary%': 0,
 
     # Enable TCMalloc.
-    'linux_use_tcmalloc%': 1,
+    'linux_use_tcmalloc%': 0,
 
     # Set to select the Title Case versions of strings in GRD files.
     'use_titlecase_in_grd_files%': 0,