tcmalloc: Use C++11 atomics where appropriate.

base/allocator/allocator.gyp

Index: base/allocator/allocator.gyp
diff --git a/base/allocator/allocator.gyp b/base/allocator/allocator.gyp
index d5ec2b64061056e95a90262e292cf1ca3e9b79f1..414e510d318d2cc466625c123a4bdf2fa84df3b5 100644
--- a/base/allocator/allocator.gyp
+++ b/base/allocator/allocator.gyp
@@ -104,13 +104,9 @@
             '<(tcmalloc_dir)/src/base/abort.cc',
             '<(tcmalloc_dir)/src/base/abort.h',
             '<(tcmalloc_dir)/src/base/arm_instruction_set_select.h',
-            '<(tcmalloc_dir)/src/base/atomicops-internals-arm-generic.h',
-            '<(tcmalloc_dir)/src/base/atomicops-internals-arm-v6plus.h',
-            '<(tcmalloc_dir)/src/base/atomicops-internals-linuxppc.h',
             '<(tcmalloc_dir)/src/base/atomicops-internals-macosx.h',
             '<(tcmalloc_dir)/src/base/atomicops-internals-windows.h',
-            '<(tcmalloc_dir)/src/base/atomicops-internals-x86.cc',
-            '<(tcmalloc_dir)/src/base/atomicops-internals-x86.h',
+            '<(tcmalloc_dir)/src/base/atomicops_internals_portable.h',
             '<(tcmalloc_dir)/src/base/atomicops.h',
             '<(tcmalloc_dir)/src/base/basictypes.h',
             '<(tcmalloc_dir)/src/base/commandlineflags.h',