Remove redundant c_str() calls.

base/trace_event/trace_config.h

Index: base/trace_event/trace_config.h
diff --git a/base/trace_event/trace_config.h b/base/trace_event/trace_config.h
index 717c2613169d3a60436df3794d3b546f5824e8b6..42fe7ba159a9c0a3cb87869121c10802970630b6 100644
--- a/base/trace_event/trace_config.h
+++ b/base/trace_event/trace_config.h
@@ -305,7 +305,7 @@ class BASE_EXPORT TraceConfig {
   // This tells whether a category is enabled from the TraceConfig's
   // perspective. Please refer to IsCategoryGroupEnabled() to determine if a
   // category is enabled from the tracing runtime's perspective.
-  bool IsCategoryEnabled(const char* category_name) const;
+  bool IsCategoryEnabled(StringPiece category_name) const;
 
   static bool IsEmptyOrContainsLeadingOrTrailingWhitespace(StringPiece str);