Don't require expectations file for DumpAccessibility tests.

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 5164717666af62e359aa94f273540293a1a151b5..87145e77850598cbaefe3bf0baebe858903be636 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -517,6 +517,12 @@ const char kForceOverlayFullscreenVideo[]   = "force-overlay-fullscreen-video";
 // overrides this if present.
 const char kForceRendererAccessibility[]    = "force-renderer-accessibility";
 
+// For development / testing only. When running content_browsertests,
+// saves output of failing accessibility tests to their expectations files in
+// content/test/data/accessibility/, overwriting existing file content.
+const char kGenerateAccessibilityTestExpectations[] =
+    "generate-accessibility-test-expectations";
+
 // Passes gpu device_id from browser process to GPU process.
 const char kGpuDeviceID[]                   = "gpu-device-id";