Reland (2) of Enable allocator shim for Android (crrev.com/1875043003)

Reason for reland:
The CL was re-reverted by crrev.com/1884223002 because it broke
the internal orderfile bot.
The reason of the breakage was the following:
 - cygprofile.cc instruments all function calls with a
   __cyg_profile_func_enter preamble.
 - __cyg_profile_func_enter uses __thread. __thread under the hoods
   invokes calloc(), on every thread, to initialize the TLS.
 - The shim layer provides its own implementation of calloc().
 - At this point, calloc() gets instrumented as well and it re-enters
   __cyg_profile_func_enter causing an infinite loop.
The key of the problem here is that __thread silently causes calls to
calloc() in a way that is out of control of cygprofile.cc.

The solution proposed by this CL is the following:
 - Don't use __thread, use explicit POSIX functions for TLS (also there
   doesn't seem to be any precendent of using __thread in the codebase).
 - Use a global variable to prevent re-entrancy of the
   __cyg_profile_func_enter in the global (once per process) TLS slot
   initializer.
 - Re-entrancy is gone.

Original issue's description:
> Enable allocator shim for Android
>
> This is a follow-up to crrev.com/1719433002, which introduced the
> shim for Android, and enables it by default by setting
> use_experimental_allocator_shim=true for Android.
>
> Build/Perf sheriffs heads up
> ----------------------------
> If you see any build error or crash related with __wrap_malloc,
> __wrap_free, __real_malloc, __real_free, etc this CL is to blame.
>
> Performance considerations
> ------------------------
> Binary size diff (GN, arm, static, official build): 24k
>
> I did a mixture of local and trybots run to estimate the perf impact
> of this change. Didn't get any conclusive data, everything I tried
> seems in the same ballpark, below noise levels. More in details:
>
> cc_perftests.PrepareTiles on a Nexus 4.
> Rationale of the choice: in a previous CL (crbug.com/593344), this
> benchmark revealed the presence of two mfences in the malloc path.
> Results: https://goo.gl/8VC3Jp in the same ballpark.
>
> page-cycler on Nexus 9 via trybots:
> Results: http://goo.gl/J3i50a seems to suggest that this CL improves
> both warm and cold times in most cases. I doubt it, more likely it's
> noise.
>
> All the other perf trybots failed. The perf waterfall seems to be in a
> bad state in these days.
>
> BUG=550886,598075
> TEST=base_unittests --gtest_filter=AllocatorShimTest.*
> TBR=thakis@chromium.org
>
> Committed: https://crrev.com/ebb95496c73dc0d5ce83968ac619921f154305f7
> Cr-Commit-Position: refs/heads/master@{#386386}

BUG=550886,598075, 602744
TBR=thakis@chromium.org
TEST=gn gen out/Debug --args='is_debug=true target_os="android" use_order_profiling=true target_cpu="arm" is_clang=false';
     ninja -C out/Debug/ cygprofile_unittests;
     adb push out/Debug/cygprofile_unittests /data/local/tmp/cygprofile_unittests_debug;
     adb shell /data/local/tmp/cygprofile_unittests_debug

Review URL: https://codereview.chromium.org/1883093005

Cr-Original-Commit-Position: refs/heads/master@{#387594}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f7a321facfdabd763ecdbc9536c890fe91c8c079

common.gypi

@@ -2274,7 +2274,7 @@
         'use_allocator%': 'none',
         'use_sanitizer_options%': 1,
       }],
-      ['OS=="linux" and asan==0 and msan==0 and lsan==0 and tsan==0 and build_for_tool==""', {
+      ['(OS=="linux" or OS=="android") and asan==0 and msan==0 and lsan==0 and tsan==0 and build_for_tool==""', {
         'use_experimental_allocator_shim%': 1,
       }],
       ['OS=="linux" and asan==0 and msan==0 and lsan==0 and tsan==0', {

config/allocator.gni

@@ -11,7 +11,7 @@ if (is_android || current_cpu == "mipsel" || is_mac || is_ios || is_asan ||
   _default_allocator = "tcmalloc"
 }
 
-if (is_linux && !is_asan && !is_lsan && !is_tsan && !is_msan) {
+if ((is_linux || is_android) && !is_asan && !is_lsan && !is_tsan && !is_msan) {
   _default_use_experimental_allocator_shim = true
 } else {
   _default_use_experimental_allocator_shim = false