Use StringPiece more in base::Value interfaces.

Many of these functions are called with string literals.
This leads to two problems:
- Implicit construction of std::string generates a
  surprising amount of code, since STL code is often
  inlined.
- We construct a temporary string, immediately copy it,
  and then throw away the original temporary.

Effect of this CL on an official Linux binary:
 before: 100.41 MiB
  after: 99.56 MiB

BUG=none

Review-Url: https://codereview.chromium.org/2278723003
Cr-Commit-Position: refs/heads/master@{#414450}

base/json/json_parser.cc

@@ -61,7 +61,7 @@ class DictionaryHiddenRootValue : public DictionaryValue {
   // Not overriding DictionaryValue::Remove because it just calls through to
   // the method below.
 
-  bool RemoveWithoutPathExpansion(const std::string& key,
+  bool RemoveWithoutPathExpansion(StringPiece key,
                                   std::unique_ptr<Value>* out) override {
     // If the caller won't take ownership of the removed value, just call up.
     if (!out)

base/values.h

@@ -149,7 +149,7 @@ class BASE_EXPORT FundamentalValue : public Value {
 class BASE_EXPORT StringValue : public Value {
  public:
   // Initializes a StringValue with a UTF-8 narrow character string.
-  explicit StringValue(const std::string& in_value);
+  explicit StringValue(StringPiece in_value);
 
   // Initializes a StringValue with a string16.
   explicit StringValue(const string16& in_value);
@@ -223,7 +223,7 @@ class BASE_EXPORT DictionaryValue : public Value {
   bool GetAsDictionary(const DictionaryValue** out_value) const override;
 
   // Returns true if the current dictionary has a value for the given key.
-  bool HasKey(const std::string& key) const;
+  bool HasKey(StringPiece key) const;
 
   // Returns the number of Values in this dictionary.
   size_t size() const { return dictionary_.size(); }
@@ -241,32 +241,31 @@ class BASE_EXPORT DictionaryValue : public Value {
   // If the key at any step of the way doesn't exist, or exists but isn't
   // a DictionaryValue, a new DictionaryValue will be created and attached
   // to the path in that location. |in_value| must be non-null.
-  void Set(const std::string& path, std::unique_ptr<Value> in_value);
+  void Set(StringPiece path, std::unique_ptr<Value> in_value);
   // Deprecated version of the above. TODO(estade): remove.
-  void Set(const std::string& path, Value* in_value);
+  void Set(StringPiece path, Value* in_value);
 
   // Convenience forms of Set().  These methods will replace any existing
   // value at that path, even if it has a different type.
-  void SetBoolean(const std::string& path, bool in_value);
-  void SetInteger(const std::string& path, int in_value);
-  void SetDouble(const std::string& path, double in_value);
-  void SetString(const std::string& path, const std::string& in_value);
-  void SetString(const std::string& path, const string16& in_value);
+  void SetBoolean(StringPiece path, bool in_value);
+  void SetInteger(StringPiece path, int in_value);
+  void SetDouble(StringPiece path, double in_value);
+  void SetString(StringPiece path, StringPiece in_value);
+  void SetString(StringPiece path, const string16& in_value);
 
   // Like Set(), but without special treatment of '.'.  This allows e.g. URLs to
   // be used as paths.
-  void SetWithoutPathExpansion(const std::string& key,
+  void SetWithoutPathExpansion(StringPiece key,
                                std::unique_ptr<Value> in_value);
   // Deprecated version of the above. TODO(estade): remove.
-  void SetWithoutPathExpansion(const std::string& key, Value* in_value);
+  void SetWithoutPathExpansion(StringPiece key, Value* in_value);
 
   // Convenience forms of SetWithoutPathExpansion().
-  void SetBooleanWithoutPathExpansion(const std::string& path, bool in_value);
-  void SetIntegerWithoutPathExpansion(const std::string& path, int in_value);
-  void SetDoubleWithoutPathExpansion(const std::string& path, double in_value);
-  void SetStringWithoutPathExpansion(const std::string& path,
-                                     const std::string& in_value);
-  void SetStringWithoutPathExpansion(const std::string& path,
+  void SetBooleanWithoutPathExpansion(StringPiece path, bool in_value);
+  void SetIntegerWithoutPathExpansion(StringPiece path, int in_value);
+  void SetDoubleWithoutPathExpansion(StringPiece path, double in_value);
+  void SetStringWithoutPathExpansion(StringPiece path, StringPiece in_value);
+  void SetStringWithoutPathExpansion(StringPiece path,
                                      const string16& in_value);
 
   // Gets the Value associated with the given path starting from this object.
@@ -284,46 +283,41 @@ class BASE_EXPORT DictionaryValue : public Value {
   // and the return value will be true if the path is valid and the value at
   // the end of the path can be returned in the form specified.
   // |out_value| is optional and will only be set if non-NULL.
-  bool GetBoolean(const std::string& path, bool* out_value) const;
-  bool GetInteger(const std::string& path, int* out_value) const;
+  bool GetBoolean(StringPiece path, bool* out_value) const;
+  bool GetInteger(StringPiece path, int* out_value) const;
   // Values of both type TYPE_INTEGER and TYPE_DOUBLE can be obtained as
   // doubles.
-  bool GetDouble(const std::string& path, double* out_value) const;
-  bool GetString(const std::string& path, std::string* out_value) const;
-  bool GetString(const std::string& path, string16* out_value) const;
-  bool GetStringASCII(const std::string& path, std::string* out_value) const;
-  bool GetBinary(const std::string& path, const BinaryValue** out_value) const;
-  bool GetBinary(const std::string& path, BinaryValue** out_value);
+  bool GetDouble(StringPiece path, double* out_value) const;
+  bool GetString(StringPiece path, std::string* out_value) const;
+  bool GetString(StringPiece path, string16* out_value) const;
+  bool GetStringASCII(StringPiece path, std::string* out_value) const;
+  bool GetBinary(StringPiece path, const BinaryValue** out_value) const;
+  bool GetBinary(StringPiece path, BinaryValue** out_value);
   bool GetDictionary(StringPiece path,
                      const DictionaryValue** out_value) const;
   bool GetDictionary(StringPiece path, DictionaryValue** out_value);
-  bool GetList(const std::string& path, const ListValue** out_value) const;
-  bool GetList(const std::string& path, ListValue** out_value);
+  bool GetList(StringPiece path, const ListValue** out_value) const;
+  bool GetList(StringPiece path, ListValue** out_value);
 
   // Like Get(), but without special treatment of '.'.  This allows e.g. URLs to
   // be used as paths.
-  bool GetWithoutPathExpansion(const std::string& key,
-                               const Value** out_value) const;
-  bool GetWithoutPathExpansion(const std::string& key, Value** out_value);
-  bool GetBooleanWithoutPathExpansion(const std::string& key,
-                                      bool* out_value) const;
-  bool GetIntegerWithoutPathExpansion(const std::string& key,
-                                      int* out_value) const;
-  bool GetDoubleWithoutPathExpansion(const std::string& key,
-                                     double* out_value) const;
-  bool GetStringWithoutPathExpansion(const std::string& key,
+  bool GetWithoutPathExpansion(StringPiece key, const Value** out_value) const;
+  bool GetWithoutPathExpansion(StringPiece key, Value** out_value);
+  bool GetBooleanWithoutPathExpansion(StringPiece key, bool* out_value) const;
+  bool GetIntegerWithoutPathExpansion(StringPiece key, int* out_value) const;
+  bool GetDoubleWithoutPathExpansion(StringPiece key, double* out_value) const;
+  bool GetStringWithoutPathExpansion(StringPiece key,
                                      std::string* out_value) const;
-  bool GetStringWithoutPathExpansion(const std::string& key,
+  bool GetStringWithoutPathExpansion(StringPiece key,
                                      string16* out_value) const;
   bool GetDictionaryWithoutPathExpansion(
-      const std::string& key,
+      StringPiece key,
       const DictionaryValue** out_value) const;
-  bool GetDictionaryWithoutPathExpansion(const std::string& key,
+  bool GetDictionaryWithoutPathExpansion(StringPiece key,
                                          DictionaryValue** out_value);
-  bool GetListWithoutPathExpansion(const std::string& key,
+  bool GetListWithoutPathExpansion(StringPiece key,
                                    const ListValue** out_value) const;
-  bool GetListWithoutPathExpansion(const std::string& key,
-                                   ListValue** out_value);
+  bool GetListWithoutPathExpansion(StringPiece key, ListValue** out_value);
 
   // Removes the Value with the specified path from this dictionary (or one
   // of its child dictionaries, if the path is more than just a local key).
@@ -331,18 +325,16 @@ class BASE_EXPORT DictionaryValue : public Value {
   // |out_value|.  If |out_value| is NULL, the removed value will be deleted.
   // This method returns true if |path| is a valid path; otherwise it will
   // return false and the DictionaryValue object will be unchanged.
-  virtual bool Remove(const std::string& path,
-                      std::unique_ptr<Value>* out_value);
+  virtual bool Remove(StringPiece path, std::unique_ptr<Value>* out_value);
 
   // Like Remove(), but without special treatment of '.'.  This allows e.g. URLs
   // to be used as paths.
-  virtual bool RemoveWithoutPathExpansion(const std::string& key,
+  virtual bool RemoveWithoutPathExpansion(StringPiece key,
                                           std::unique_ptr<Value>* out_value);
 
   // Removes a path, clearing out all dictionaries on |path| that remain empty
   // after removing the value at |path|.
-  virtual bool RemovePath(const std::string& path,
-                          std::unique_ptr<Value>* out_value);
+  virtual bool RemovePath(StringPiece path, std::unique_ptr<Value>* out_value);
 
   // Makes a copy of |this| but doesn't include empty dictionaries and lists in
   // the copy.  This never returns NULL, even if |this| itself is empty.
@@ -472,7 +464,7 @@ class BASE_EXPORT ListValue : public Value {
   void AppendBoolean(bool in_value);
   void AppendInteger(int in_value);
   void AppendDouble(double in_value);
-  void AppendString(const std::string& in_value);
+  void AppendString(StringPiece in_value);
   void AppendString(const string16& in_value);
   void AppendStrings(const std::vector<std::string>& in_values);
   void AppendStrings(const std::vector<string16>& in_values);

chrome/browser/ui/webui/plugins/plugins_handler.cc

@@ -171,7 +171,7 @@ void PluginsPageHandler::SetPluginAlwaysAllowed(const mojo::String& plugin,
   // whitelisted by the user from automatically whitelisted ones.
   DictionaryPrefUpdate update(profile->GetPrefs(),
                               prefs::kContentSettingsPluginWhitelist);
-  update->SetBoolean(plugin, allowed);
+  update->SetBoolean(plugin.get(), allowed);
 }
 
 void PluginsPageHandler::GetPluginsData(

components/arc/net/arc_net_host_impl.cc

@@ -450,7 +450,8 @@ void ArcNetHostImpl::CreateNetwork(mojom::WifiConfigurationPtr cfg,
 
   properties->SetStringWithoutPathExpansion(onc::network_config::kType,
                                             onc::network_config::kWiFi);
-  wifi_dict->SetStringWithoutPathExpansion(onc::wifi::kHexSSID, cfg->hexssid);
+  wifi_dict->SetStringWithoutPathExpansion(onc::wifi::kHexSSID,
+                                           cfg->hexssid.get());
   wifi_dict->SetBooleanWithoutPathExpansion(onc::wifi::kAutoConnect,
                                             details->autoconnect);
   if (cfg->security.get().empty()) {
@@ -458,10 +459,10 @@ void ArcNetHostImpl::CreateNetwork(mojom::WifiConfigurationPtr cfg,
                                              onc::wifi::kSecurityNone);
   } else {
     wifi_dict->SetStringWithoutPathExpansion(onc::wifi::kSecurity,
-                                             cfg->security);
+                                             cfg->security.get());
     if (!details->passphrase.is_null()) {
       wifi_dict->SetStringWithoutPathExpansion(onc::wifi::kPassphrase,
-                                               details->passphrase);
+                                               details->passphrase.get());
     }
   }
   properties->SetWithoutPathExpansion(onc::network_config::kWiFi,

components/domain_reliability/context_unittest.cc

@@ -13,6 +13,7 @@
 
 #include "base/bind.h"
 #include "base/json/json_reader.h"
+#include "base/strings/string_piece.h"
 #include "components/domain_reliability/beacon.h"
 #include "components/domain_reliability/dispatcher.h"
 #include "components/domain_reliability/scheduler.h"
@@ -60,8 +61,8 @@ std::unique_ptr<DomainReliabilityBeacon> MakeBeacon(MockableTime* time) {
 }
 
 template <typename ValueType,
-          bool (DictionaryValue::* GetValueType)(const std::string&,
-                                                 ValueType*) const>
+          bool (DictionaryValue::*GetValueType)(base::StringPiece, ValueType*)
+              const>
 struct HasValue {
   bool operator()(const DictionaryValue& dict,
                   const std::string& key,