Move StartsWith[ASCII] to base namespace.

tools/clang/blink_gc_plugin/Config.h

Index: tools/clang/blink_gc_plugin/Config.h
diff --git a/tools/clang/blink_gc_plugin/Config.h b/tools/clang/blink_gc_plugin/Config.h
index 197e294f76a48dc0c2aa2fd3c8e19b4f0ae8efcb..294e08645e5b98ce1b612ad1ca79e4ca3e023141 100644
--- a/tools/clang/blink_gc_plugin/Config.h
+++ b/tools/clang/blink_gc_plugin/Config.h
@@ -253,7 +253,8 @@ class Config {
     return name == kTraceImplName || name == kTraceAfterDispatchImplName;
   }
 
-  static bool StartsWith(const std::string& str, const std::string& prefix) {
+  static bool base::StartsWith(const std::string& str,
+                               const std::string& prefix) {
     if (prefix.size() > str.size())
       return false;
     return str.compare(0, prefix.size(), prefix) == 0;