Restore the -fvisibility=hidden flag for tcmalloc when using allocator shim.

base/allocator/allocator.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'target_defaults': {
     'variables': {
       # This code gets run a lot and debugged rarely, so it should be fast
       # by default. See http://crbug.com/388949.
       'debug_optimize': '2',
@@ skipping 283 matching lines @@
               'sources!': [
                 '<(tcmalloc_dir)/src/system-alloc.h',
               ],
               # We enable all warnings by default, but upstream disables a few.
               # Keep "-Wno-*" flags in sync with upstream by comparing against:
               # http://code.google.com/p/google-perftools/source/browse/trunk/Makefile.am
               'cflags': [
                 '-Wno-sign-compare',
                 '-Wno-unused-result',
               ],
-              'cflags!': [
-                '-fvisibility=hidden',
-              ],
               'link_settings': {
                 'ldflags': [
                   # Don't let linker rip this symbol out, otherwise the heap&cpu
                   # profilers will not initialize properly on startup.
                   '-Wl,-uIsHeapProfilerRunning,-uProfilerStart',
                   # Do the same for heap leak checker.
                   '-Wl,-u_Z21InitialMallocHook_NewPKvj,-u_Z22InitialMallocHook_MMapPKvS0_jiiix,-u_Z22InitialMallocHook_SbrkPKvi',
                   '-Wl,-u_Z21InitialMallocHook_NewPKvm,-u_Z22InitialMallocHook_MMapPKvS0_miiil,-u_Z22InitialMallocHook_SbrkPKvl',
                   '-Wl,-u_ZN15HeapLeakChecker12IgnoreObjectEPKv,-u_ZN15HeapLeakChecker14UnIgnoreObjectEPKv',
                 ],
               },
+              # Compiling tcmalloc with -fvisibility=default is only necessary when
+              # not using the allocator shim, which provides the correct visibility
+              # annotations for those symbols which need to be exported (see
+              # //base/allocator/allocator_shim_override_glibc_weak_symbols.h and
+              # //base/allocator/allocator_shim_internals.h for the definition of
+              # SHIM_ALWAYS_EXPORT).
+              'conditions': [
+                ['use_experimental_allocator_shim==0', {
+                  'cflags!': [
+                    '-fvisibility=hidden',
+                  ],
+                }],
+              ],
             }],
             ['profiling!=1', {
               'sources!': [
                 # cpuprofiler
                 '<(tcmalloc_dir)/src/base/thread_lister.c',
                 '<(tcmalloc_dir)/src/base/thread_lister.h',
                 '<(tcmalloc_dir)/src/profile-handler.cc',
                 '<(tcmalloc_dir)/src/profile-handler.h',
                 '<(tcmalloc_dir)/src/profiledata.cc',
                 '<(tcmalloc_dir)/src/profiledata.h',
@@ skipping 103 matching lines @@
                   '-Wl,-wrap,valloc',
                 ],
               },
             }],
           ]
         },  # 'unified_allocator_shim' target.
       ],
     }]
   ],
 }