Skip base::string16 if not necessary for WebString <-> ASCII conversion

media/blink/key_system_config_selector.cc

Index: media/blink/key_system_config_selector.cc
diff --git a/media/blink/key_system_config_selector.cc b/media/blink/key_system_config_selector.cc
index 06e308ca21e6eeb2edc007121908576bbeeb411f..a4f2b27b05dccd6ce2931161b4a2eb20eb9a0c39 100644
--- a/media/blink/key_system_config_selector.cc
+++ b/media/blink/key_system_config_selector.cc
@@ -402,12 +402,9 @@ bool KeySystemConfigSelector::GetSupportedCapabilities(
     ConfigState proposed_config_state = *config_state;
     if (!base::IsStringASCII(capability.mimeType) ||
         !base::IsStringASCII(capability.codecs) ||
-        !IsSupportedContentType(key_system, media_type,
-                                base::UTF16ToASCII(
-                                    base::StringPiece16(capability.mimeType)),
-                                base::UTF16ToASCII(
-                                    base::StringPiece16(capability.codecs)),
-                                &proposed_config_state)) {
+        !IsSupportedContentType(
+            key_system, media_type, capability.mimeType.ascii(),
+            capability.codecs.ascii(), &proposed_config_state)) {
       continue;
     }
     // 3.12. If robustness is not the empty string, run the following steps:
@@ -418,8 +415,7 @@ bool KeySystemConfigSelector::GetSupportedCapabilities(
       if (!base::IsStringASCII(capability.robustness))
         continue;
       EmeConfigRule robustness_rule = key_systems_->GetRobustnessConfigRule(
-          key_system, media_type, base::UTF16ToASCII(
-              base::StringPiece16(capability.robustness)));
+          key_system, media_type, capability.robustness.ascii());
       if (!proposed_config_state.IsRuleSupported(robustness_rule))
         continue;
       proposed_config_state.AddRule(robustness_rule);
@@ -838,13 +834,12 @@ void KeySystemConfigSelector::SelectConfig(
   // 6.1 If keySystem is not one of the Key Systems supported by the user
   //     agent, reject promise with a NotSupportedError. String comparison
   //     is case-sensitive.
-  if (!base::IsStringASCII(key_system)) {
+  if (!key_system.containsOnlyASCII()) {
     not_supported_cb.Run("Only ASCII keySystems are supported");
     return;
   }
 
-  std::string key_system_ascii =
-      base::UTF16ToASCII(base::StringPiece16(key_system));
+  std::string key_system_ascii = key_system.ascii();
   if (!key_systems_->IsSupportedKeySystem(key_system_ascii)) {
     not_supported_cb.Run("Unsupported keySystem");
     return;