New SkRTConf macro SK_CONF_TRY_SET: no complaint on missing configuration

include/utils/SkRTConf.h

Index: include/utils/SkRTConf.h
diff --git a/include/utils/SkRTConf.h b/include/utils/SkRTConf.h
index d09410ebb17dc256a972e2e2feabcdf6d7780088..4d7cda23d599508d1aad66505346812eddcebb01 100644
--- a/include/utils/SkRTConf.h
+++ b/include/utils/SkRTConf.h
@@ -52,10 +52,17 @@ protected:
 
 #ifdef SK_DEVELOPER
 #define SK_CONF_DECLARE(confType, varName, confName, defaultValue, description) static SkRTConf<confType> varName(confName, defaultValue, description)
-#define SK_CONF_SET(confname, value) skRTConfRegistry().set(confname, value)
+#define SK_CONF_SET(confname, value) \
+    skRTConfRegistry().set(confname, value, true)
+/* SK_CONF_TRY_SET() is like SK_CONF_SET(), but doesn't complain if
+   confname can't be found.  This is useful if the SK_CONF_DECLARE is
+   inside a source file whose linkage is dependent on the system. */
+#define SK_CONF_TRY_SET(confname, value) \
+    skRTConfRegistry().set(confname, value, false)
 #else
 #define SK_CONF_DECLARE(confType, varName, confName, defaultValue, description) static confType varName = defaultValue
 #define SK_CONF_SET(confname, value) (void) confname, (void) value
+#define SK_CONF_TRY_SET(confname, value) (void) confname, (void) value
 #endif
 
 /** \class SkRTConfRegistry
@@ -72,7 +79,9 @@ public:
     const char *configFileLocation() const;
     void possiblyDumpFile() const;
     void validate() const;
-    template <typename T> void set(const char *confname, T value);
+    template <typename T> void set(const char *confname,
+                                   T value,
+                                   bool warnIfNotFound = true);
 #ifdef SK_SUPPORT_UNITTEST
     static void UnitTest();
 #endif