Remove using directives ("using namespace x") from tools/binary_size/.

Bug: 82078
Change-Id: Iba91aaf15643c3a3ca9ebbfc930bec634b6eda14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1886170
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710329}

tools/binary_size/libsupersize/caspian/model.cc

@@ -10,7 +10,7 @@
 
 #include "tools/binary_size/libsupersize/caspian/file_format.h"
 
-using namespace caspian;
+namespace caspian {
 
 Symbol::Symbol() = default;
 Symbol::Symbol(const Symbol& other) = default;
@@ -128,3 +128,5 @@ SectionId NodeStats::ComputeBiggestSection() const {
   }
   return ret;
 }
+
+}  // namespace caspian