Remove legacy StartsWithASCII function.

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index b060993bc86b60f4deef82fbd628feecf78464c1..6fb58a9d7ff419a3dcbaa323da035448f173cd3f 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -2991,7 +2991,8 @@ extern NSString *NSTextInputReplacementRangeAttributeName;
     // We ignore commands that insert characters, because this was causing
     // strange behavior (e.g. tab always inserted a tab rather than moving to
     // the next field on the page).
-    if (!base::StartsWithASCII(command, "insert", false))
+    if (!base::StartsWith(command, "insert",
+                          base::CompareCase::INSENSITIVE_ASCII))
       editCommands_.push_back(EditCommand(command, ""));
   } else {
     RenderWidgetHostImpl* rwh = renderWidgetHostView_->render_widget_host_;