Mac: exit browser fullscreen on Esc

Every (non-Chrome) Mac app I've tried supports this, and nobody seems to
know of a good reason for why we don't do it, so let's do it.

Bug: 1074609
Change-Id: I43e9b5137faf347e17e737e2e3f2cbdba4e6c470
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2174345Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#764644}

chrome/browser/ui/exclusive_access/fullscreen_controller.cc

@@ -274,10 +274,14 @@ bool FullscreenController::HandleUserPressedEscape() {
     return true;
   }
 
+// On macOS, it's idiomatic to exit application fullscreen on Esc.
+#if !defined(OS_MACOSX)
   if (!IsWindowFullscreenForTabOrPending())
     return false;
-
-  ExitExclusiveAccessIfNecessary();
+  ExitFullscreenModeForTab(exclusive_access_tab());
+#else
+  ExitExclusiveAccessToPreviousState();
+#endif
   return true;
 }