chore: migrate base::StringPiece to std::string_view (#40915)

* chore: migrate from base::StringPiece to std::string_view in keyboard_util.cc

* chore: migrate from base::StringPiece to std::string_view in error_thrower.cc

* chore: migrate from base::StringPiece to std::string_view in electron_api_web_contents.cc

* chore: migrate from base::StringPiece to std::string_view in gin_helper/dictionary.h

* chore: migrate from base::StringPiece to std::string_view in electron_api_url_loader.cc

* chore: phase out internal use of base:::StringPiece

`base::StringPiece` is being phased out upstream. Its code has been
removed upstream and it's just a typedef for `std::string_view`.

They haven't removed the typedef yet, so this PR tries to get ahead
of future breakage by migrating "internal" use (i.e. leaving alone the
places where the `base::StringPiece` name is coming from an upstream
method that we override).

Xref: https://bugs.chromium.org/p/chromium/issues/detail?id=691162

Xref: 4294483

Xref: https://docs.google.com/document/d/1d4RnD1uAE2t4iANR0nXy82ASIPGsPuw2mpO6v6T7JKs

shell/renderer/api/electron_api_web_frame.cc

@@ -5,6 +5,7 @@
 #include <limits>
 #include <memory>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <vector>
 
@@ -397,7 +398,7 @@ class WebFrameRenderer : public gin::Wrappable<WebFrameRenderer>,
 
  private:
   bool MaybeGetRenderFrame(v8::Isolate* isolate,
-                           const base::StringPiece method_name,
+                           const std::string_view method_name,
                            content::RenderFrame** render_frame_ptr) {
     std::string error_msg;
     if (!MaybeGetRenderFrame(&error_msg, method_name, render_frame_ptr)) {
@@ -408,7 +409,7 @@ class WebFrameRenderer : public gin::Wrappable<WebFrameRenderer>,
   }
 
   bool MaybeGetRenderFrame(std::string* error_msg,
-                           const base::StringPiece method_name,
+                           const std::string_view method_name,
                            content::RenderFrame** render_frame_ptr) {
     auto* frame = render_frame();
     if (!frame) {