build,[win]: fix ambiguous reference with MSSTL

size is defined in `<xutility>` with VS 2019

Bug: none
Change-Id: I337599b8808f36d2c2c3ad1b327352d440c9dea3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879683
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710491}

base/command_line.cc

@@ -43,7 +43,7 @@ constexpr CommandLine::StringPieceType kSwitchPrefixes[] = {L"--", L"-", L"/"};
 // Unixes don't use slash as a switch.
 constexpr CommandLine::StringPieceType kSwitchPrefixes[] = {"--", "-"};
 #endif
-size_t switch_prefix_count = size(kSwitchPrefixes);
+size_t switch_prefix_count = base::size(kSwitchPrefixes);
 
 size_t GetSwitchPrefixLength(CommandLine::StringPieceType string) {
   for (size_t i = 0; i < switch_prefix_count; ++i) {
@@ -201,7 +201,7 @@ void CommandLine::set_slash_is_not_a_switch() {
   // The last switch prefix should be slash, so adjust the size to skip it.
   static_assert(base::make_span(kSwitchPrefixes).back() == L"/",
                 "Error: Last switch prefix is not a slash.");
-  switch_prefix_count = size(kSwitchPrefixes) - 1;
+  switch_prefix_count = base::size(kSwitchPrefixes) - 1;
 }
 
 // static