Take a StringPiece when looking up CommandLine switches.

base/command_line.h

Index: base/command_line.h
diff --git a/base/command_line.h b/base/command_line.h
index 19df40c4c478bfa9befe59ad9eefc63f5b33c55f..48b54ea80a6104c1834eacb607c25a0ba580ae52 100644
--- a/base/command_line.h
+++ b/base/command_line.h
@@ -22,6 +22,7 @@
 
 #include "base/base_export.h"
 #include "base/strings/string16.h"
+#include "base/strings/string_piece.h"
 #include "build/build_config.h"
 
 namespace base {
@@ -52,6 +53,10 @@ class BASE_EXPORT CommandLine {
   CommandLine(int argc, const CharType* const* argv);
   explicit CommandLine(const StringVector& argv);
 
+  // Override copy and assign to ensure |switches_by_stringpiece_| is valid.
+  CommandLine(const CommandLine& other);
+  CommandLine& operator=(const CommandLine& other);
+
   ~CommandLine();
 
 #if defined(OS_WIN)
@@ -142,19 +147,20 @@ class BASE_EXPORT CommandLine {
   void SetProgram(const FilePath& program);
 
   // Returns true if this command line contains the given switch.
-  // (Switch names are case-insensitive).
+  // Switch names must be lowercase.
   // The second override provides an optimized version to avoid inlining the
-  // codegen for the string allocation.
-  bool HasSwitch(const std::string& switch_string) const;
+  // codegen to find the length of the constant and construct a StringPiece.
+  bool HasSwitch(const base::StringPiece& switch_string) const;
   bool HasSwitch(const char switch_constant[]) const;
 
   // Returns the value associated with the given switch. If the switch has no
   // value or isn't present, this method returns the empty string.
-  std::string GetSwitchValueASCII(const std::string& switch_string) const;
-  FilePath GetSwitchValuePath(const std::string& switch_string) const;
-  StringType GetSwitchValueNative(const std::string& switch_string) const;
+  // Switch names must be lowercase.
+  std::string GetSwitchValueASCII(const base::StringPiece& switch_string) const;
+  FilePath GetSwitchValuePath(const base::StringPiece& switch_string) const;
+  StringType GetSwitchValueNative(const base::StringPiece& switch_string) const;
 
-  // Get a copy of all switches, along with their values.
+  // Get a reference to the internal switch map.
   const SwitchMap& GetSwitches() const { return switches_; }
 
   // Append a switch [with optional value] to the command line.
@@ -223,6 +229,12 @@ class BASE_EXPORT CommandLine {
   // Parsed-out switch keys and values.
   SwitchMap switches_;
 
+  // A mirror of |switches_| with only references to the actual strings.
+  // The StringPiece internally holds a pointer to a key in |switches_| while
+  // the mapped_type points to a value in |switches_|.
+  // Used for allocation-free lookups.
+  std::map<base::StringPiece, const StringType*> switches_by_stringpiece_;
+
   // The index after the program and switches, any arguments start here.
   size_t begin_args_;
 };