[Mac stack sampler] Re-enable stack sampler on Canary and unbranded builds

The impact on browser tests runtime should be fixed by
https://chromium-review.googlesource.com/c/571277

Bug: 531673
Change-Id: Ie60229d1f26c587a1ef092b99d3412cc8235488d
Reviewed-on: https://chromium-review.googlesource.com/574868Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487252}

chrome/common/stack_sampling_configuration.cc

@@ -30,8 +30,12 @@ bool IsProfilerSupported() {
     return true;
   #endif
 #elif defined(OS_MACOSX)
-  // Disabled due to suspected CQ impact: crbug.com/723108#c23
-  return false;
+  // Only run on canary for now.
+  #if defined(GOOGLE_CHROME_BUILD)
+    return chrome::GetChannel() == version_info::Channel::CANARY;
+  #else
+    return true;
+  #endif
 #else
   return false;
 #endif