Migrate to OS_MAC

This migrates:

 defined(OS_MACOSX) && !defined(OS_IOS) -> defined(OS_MAC)

Bug: 1105907
Change-Id: Ib9e0314c5c15cf33b86ed98cbd2d46a454a9b719
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2331856
Auto-Submit: Avi Drissman <avi@chromium.org>
Commit-Queue: Primiano Tucci <primiano@chromium.org>
Reviewed-by: Primiano Tucci <primiano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793528}

services/tracing/public/cpp/stack_sampling/tracing_sampler_profiler_unittest.cc

@@ -26,7 +26,7 @@
 #include "services/tracing/public/cpp/stack_sampling/loader_lock_sampler_win.h"
 #endif
 
-#if defined(OS_MACOSX) && !defined(OS_IOS)
+#if defined(OS_MAC)
 #include "base/mac/mac_util.h"
 #endif
 
@@ -184,7 +184,7 @@ class TestModule : public base::ModuleCache::Module {
 };
 
 bool ShouldSkipTestForMacOS11() {
-#if defined(OS_MACOSX) && !defined(OS_IOS)
+#if defined(OS_MAC)
   // The sampling profiler does not work on macOS 11 and is disabled.
   // See https://crbug.com/1101399 and https://crbug.com/1098119.
   // DCHECK here so that when the sampling profiler is re-enabled on macOS 11,