tcmalloc_unittest: Use malloc and free directly, instead of tc_malloc and tc_free.

tcmalloc defines malloc and free as wrappers (or aliases) for tc_malloc
and tc_free, so we can test tcmalloc by using malloc and free directly
instead of tc_malloc and tc_free. This fixes the test in component
builds, where tc_malloc and tc_free are defined in a separate DSO with
hidden visibility (due to https://codereview.chromium.org/2019183002/),
and so will not be visible to tests.

Some compilers (e.g. clang) will specifically recognize and optimize
away calls to malloc and free, which would break these tests, as
they are testing specific behavior of the allocator. Address this by
marking the wrappers for malloc and free as NOINLINE.

BUG=
TBR=primiano@chromium.org

Review-Url: https://codereview.chromium.org/2028183002
Cr-Commit-Position: refs/heads/master@{#397204}

base/allocator/tcmalloc_unittest.cc

@@ -5,28 +5,27 @@
 #include <stddef.h>
 #include <stdio.h>
 
+#include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/process/process_metrics.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 #if defined(USE_TCMALLOC)
-extern "C" {
-void* tc_malloc(size_t size);
-void tc_free(void*);
-}
-
 namespace {
 
 using std::min;
 
 #ifdef NDEBUG
-void* TCMallocDoMallocForTest(size_t size) {
-  return tc_malloc(size);
+// We wrap malloc and free in noinline functions to ensure that we test the real
+// implementation of the allocator. Otherwise, the compiler may specifically
+// recognize the calls to malloc and free in our tests and optimize them away.
+NOINLINE void* TCMallocDoMallocForTest(size_t size) {
+  return malloc(size);
 }
 
-void TCMallocDoFreeForTest(void* ptr) {
-  tc_free(ptr);
+NOINLINE void TCMallocDoFreeForTest(void* ptr) {
+  free(ptr);
 }
 #endif