Add config options to run different GPU APIs to dm and nanobench

tools/flags/SkCommandLineFlags.h

Index: tools/flags/SkCommandLineFlags.h
diff --git a/tools/flags/SkCommandLineFlags.h b/tools/flags/SkCommandLineFlags.h
index 5909413523143f87fd9d25eab0d565a37d82c082..7b931981b008a4910fed4333525bb24cbfbb5d20 100644
--- a/tools/flags/SkCommandLineFlags.h
+++ b/tools/flags/SkCommandLineFlags.h
@@ -204,7 +204,15 @@ SK_UNUSED static bool unused_##name = SkFlagInfo::CreateStringFlag(TO_STRING(nam
                                                                    nullptr,              \
                                                                    &FLAGS_##name,     \
                                                                    defaultValue,      \
-                                                                   helpString)
+                                                                   helpString, nullptr)
+#define DEFINE_extended_string(name, defaultValue, helpString, extendedHelpString) \
+SkCommandLineFlags::StringArray FLAGS_##name;                                      \
+SK_UNUSED static bool unused_##name = SkFlagInfo::CreateStringFlag(TO_STRING(name),   \
+                                                                   nullptr, \
+                                                                   &FLAGS_##name, \
+                                                                   defaultValue, \
+                                                                   helpString, \
+                                                                   extendedHelpString)
 
 // string2 allows specifying a short name. There is an assert that shortName
 // is only 1 character.
@@ -214,7 +222,7 @@ SK_UNUSED static bool unused_##name = SkFlagInfo::CreateStringFlag(TO_STRING(nam
                                                                    TO_STRING(shortName),  \
                                                                    &FLAGS_##name,         \
                                                                    defaultValue,          \
-                                                                   helpString)
+                                                                   helpString, nullptr)
 
 #define DECLARE_string(name) extern SkCommandLineFlags::StringArray FLAGS_##name;
 
@@ -273,7 +281,7 @@ public:
      */
     static bool CreateBoolFlag(const char* name, const char* shortName, bool* pBool,
                                bool defaultValue, const char* helpString) {
-        SkFlagInfo* info = new SkFlagInfo(name, shortName, kBool_FlagType, helpString);
+        SkFlagInfo* info = new SkFlagInfo(name, shortName, kBool_FlagType, helpString, nullptr);
         info->fBoolValue = pBool;
         *info->fBoolValue = info->fDefaultBool = defaultValue;
         return true;
@@ -287,14 +295,15 @@ public:
      */
     static bool CreateStringFlag(const char* name, const char* shortName,
                                  SkCommandLineFlags::StringArray* pStrings,
-                                 const char* defaultValue, const char* helpString);
+                                 const char* defaultValue, const char* helpString,
+                                 const char* extendedHelpString);
 
     /**
      *  See comments for CreateBoolFlag.
      */
     static bool CreateIntFlag(const char* name, int32_t* pInt,
                               int32_t defaultValue, const char* helpString) {
-        SkFlagInfo* info = new SkFlagInfo(name, nullptr, kInt_FlagType, helpString);
+        SkFlagInfo* info = new SkFlagInfo(name, nullptr, kInt_FlagType, helpString, nullptr);
         info->fIntValue = pInt;
         *info->fIntValue = info->fDefaultInt = defaultValue;
         return true;
@@ -302,7 +311,7 @@ public:
 
     static bool CreateIntFlag(const char* name, const char* shortName, int32_t* pInt,
                               int32_t defaultValue, const char* helpString) {
-        SkFlagInfo* info = new SkFlagInfo(name, shortName, kInt_FlagType, helpString);
+        SkFlagInfo* info = new SkFlagInfo(name, shortName, kInt_FlagType, helpString, nullptr);
         info->fIntValue = pInt;
         *info->fIntValue = info->fDefaultInt = defaultValue;
         return true;
@@ -313,7 +322,7 @@ public:
      */
     static bool CreateDoubleFlag(const char* name, double* pDouble,
                                  double defaultValue, const char* helpString) {
-        SkFlagInfo* info = new SkFlagInfo(name, nullptr, kDouble_FlagType, helpString);
+        SkFlagInfo* info = new SkFlagInfo(name, nullptr, kDouble_FlagType, helpString, nullptr);
         info->fDoubleValue = pDouble;
         *info->fDoubleValue = info->fDefaultDouble = defaultValue;
         return true;
@@ -383,6 +392,7 @@ public:
     const SkString& shortName() const { return fShortName; }
 
     const SkString& help() const { return fHelpString; }
+    const SkString& extendedHelp() const { return fExtendedHelpString; }
 
     SkString defaultValue() const {
         SkString result;
@@ -421,11 +431,12 @@ public:
     }
 
 private:
-    SkFlagInfo(const char* name, const char* shortName, FlagTypes type, const char* helpString)
+    SkFlagInfo(const char* name, const char* shortName, FlagTypes type, const char* helpString, const char* extendedHelpString)
         : fName(name)
         , fShortName(shortName)
         , fFlagType(type)
         , fHelpString(helpString)
+        , fExtendedHelpString(extendedHelpString)
         , fBoolValue(nullptr)
         , fDefaultBool(false)
         , fIntValue(nullptr)
@@ -453,6 +464,7 @@ private:
     SkString             fShortName;
     FlagTypes            fFlagType;
     SkString             fHelpString;
+    SkString             fExtendedHelpString;
     bool*                fBoolValue;
     bool                 fDefaultBool;
     int32_t*             fIntValue;