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

base/allocator/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/buildflag_header.gni")
 import("//build/config/allocator.gni")
 import("//build/config/compiler/compiler.gni")
 
 declare_args() {
   # Provide a way to force disable debugallocation in Debug builds,
@@ skipping 218 matching lines @@
       ]
 
       # 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",
       ]
 
-      configs -= [ "//build/config/gcc:symbol_visibility_hidden" ]
-      configs += [ "//build/config/gcc:symbol_visibility_default" ]
+      # 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).
+      if (!use_experimental_allocator_shim) {
+        configs -= [ "//build/config/gcc:symbol_visibility_hidden" ]
+        configs += [ "//build/config/gcc:symbol_visibility_default" ]
+      }
 
       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",
@@ skipping 55 matching lines @@
       sources += [ "allocator_shim_default_dispatch_to_glibc.cc" ]
     } else if (is_android && use_allocator == "none") {
       sources += [
         "allocator_shim_default_dispatch_to_linker_wrapped_symbols.cc",
         "allocator_shim_override_linker_wrapped_symbols.h",
       ]
       all_dependent_configs = [ ":wrap_malloc_symbols" ]
     }
   }
 }