[jumbo] resolve ::switches / ::extensions::switches confusion

There is both a top level namespace ::switches and a sub
namespace ::extensions::switches so inside extensions,
if both namespaces are known to the compiler, you need to
clarify which one you want. This is the reason the code
style guide prohibits sub namespaces with the same name as
common top level namespaces.

This is a quick fix to make some jumbo builds happy. I am not sure
exactly what commit triggered this, but it can easily happen just
by adding an include somewhere.

TBR=hubbe@chromium.org

Change-Id: I22d742aa1645aa1b37317524e9b1aa18e91d2fd3
Reviewed-on: https://chromium-review.googlesource.com/c/1303362Reviewed-by: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#603452}

chrome/browser/ui/webui/extensions/extensions_ui.cc

@@ -321,7 +321,7 @@ content::WebUIDataSource* CreateMdExtensionsSource(bool in_dev_mode) {
   source->AddBoolean(kInDevModeKey, in_dev_mode);
   source->AddBoolean(kShowActivityLogKey,
                      base::CommandLine::ForCurrentProcess()->HasSwitch(
-                         switches::kEnableExtensionActivityLogging));
+                         ::switches::kEnableExtensionActivityLogging));
   source->AddString(kLoadTimeClassesKey, GetLoadTimeClasses(in_dev_mode));
 
 #if BUILDFLAG(OPTIMIZE_WEBUI)