SkPDF: fix pessimizing-move in PDFA code

src/pdf/SkPDFMetadata.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMilestone.h"
 #include "SkPDFMetadata.h"
 #include "SkPDFTypes.h"
@@ skipping 104 matching lines @@
     length = _vscprintf(format, args);
     va_end(args);
 
     SkString string((size_t)length);
     va_start(args, format);
     SkDEBUGCODE(int check = ) _vsnprintf_s(string.writable_str(), length + 1,
                                            _TRUNCATE, format, args);
     va_end(args);
     SkASSERT(check == length);
     SkASSERT(string[length] == '\0');
-    return std::move(string);
+    return string;
 #else  // C99/C++11 standard vsnprintf
     // TODO: When all compilers support this, remove windows-specific code.
     va_list args;
     va_start(args, format);
     char buffer[1024];
     int length = vsnprintf(buffer, sizeof(buffer), format, args);
     va_end(args);
     if (length < 0) {
         return SkString();
     }
     if (length < (int)sizeof(buffer)) {
         return SkString(buffer, length);
     }
     SkString string((size_t)length);
     va_start(args, format);
     SkDEBUGCODE(int check = )
             vsnprintf(string.writable_str(), length + 1, format, args);
     va_end(args);
     SkASSERT(check == length);
     SkASSERT(string[length] == '\0');
-    return std::move(string);
+    return string;
 #endif
 }
 
 static const SkString get(const SkTArray<SkDocument::Attribute>& info,
                           const char* key) {
     for (const auto& keyValue : info) {
         if (keyValue.fKey.equals(key)) {
             return keyValue.fValue;
         }
     }
@@ skipping 191 matching lines @@
             creator.c_str(), title.c_str(),
             subject.c_str(), author.c_str(), keywords1.c_str(),
             documentID.c_str(), instanceID.c_str(), keywords2.c_str()));
 }
 
 #endif  // SK_PDF_GENERATE_PDFA
 
 #undef SKPDF_STRING
 #undef SKPDF_STRING_IMPL