Make CSSSyntaxDescriptor constructor explicit and not bump string ref…

… count.

It's not clear that much is gained by passing by value here (the inner functions
use const references), and in any event, single-argument constructors should
be explicit unless it's intended that they be used for implicit conversion.

Change-Id: I0e4d0824dadfd8ef4de1ea513bf48059612ac53a
Reviewed-on: https://chromium-review.googlesource.com/655858
Reviewed-by: meade_UTC10 <meade@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501132}

third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.cpp

@@ -89,7 +89,7 @@ bool ConsumeSyntaxIdent(const String& input, size_t& offset, String& ident) {
   return !CSSPropertyParserHelpers::IsCSSWideKeyword(ident);
 }
 
-CSSSyntaxDescriptor::CSSSyntaxDescriptor(String input) {
+CSSSyntaxDescriptor::CSSSyntaxDescriptor(const String& input) {
   size_t offset = 0;
   ConsumeWhitespace(input, offset);
 

third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h

@@ -46,7 +46,7 @@ struct CSSSyntaxComponent {
 
 class CORE_EXPORT CSSSyntaxDescriptor {
  public:
-  CSSSyntaxDescriptor(String syntax);
+  explicit CSSSyntaxDescriptor(const String& syntax);
 
   const CSSValue* Parse(CSSParserTokenRange,
                         const CSSParserContext*,