Remove default arguments on WebContents(Impl)::StartPrerendering

The default arguments on virtual and override methods are prohibited by
clang-tidy/google-default-arguments [1][2].
This CL removes them from WebContents(Impl)::StartPrerendering.

[1] https://clang.llvm.org/extra/clang-tidy/checks/google/default-arguments.html
[2] https://google.github.io/styleguide/cppguide.html#Default_Arguments

Bug: n/a
Change-Id: Iec33c86ee4d19b651354155fec129b4d69bbd855
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5385581
Reviewed-by: Avi Drissman <[email protected]>
Commit-Queue: Taiyo Mizuhashi <[email protected]>
Reviewed-by: Hiroki Nakagawa <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1276176}
diff --git a/content/public/browser/web_contents.h b/content/public/browser/web_contents.h
index 6632304..30ec33c4c 100644
--- a/content/public/browser/web_contents.h
+++ b/content/public/browser/web_contents.h
@@ -1485,9 +1485,9 @@
       ui::PageTransition page_transition,
       PreloadingHoldbackStatus holdback_status_override,
       PreloadingAttempt* preloading_attempt,
-      base::RepeatingCallback<bool(const GURL&)> url_match_predicate = {},
+      base::RepeatingCallback<bool(const GURL&)> url_match_predicate,
       base::RepeatingCallback<void(NavigationHandle&)>
-          prerender_navigation_handle_callback = {}) = 0;
+          prerender_navigation_handle_callback) = 0;
 
   // May be called when the embedder believes that it is likely that the user
   // will perform a back navigation due to the trigger indicated by `predictor`