pdfviewer: code cleanup - remove STL usage

experimental/PdfViewer/SkPdfUtils.cpp

 #include "SkPdfUtils.h"
 
+bool operator !=(const SkString& first, const char* second) {
+    return !first.equals(second);
+}
+
 #ifdef PDF_TRACE
 void SkTraceMatrix(const SkMatrix& matrix, const char* sz) {
     printf("SkMatrix %s ", sz);
     for (int i = 0 ; i < 9 ; i++) {
         printf("%f ", SkScalarToDouble(matrix.get(i)));
     }
     printf("\n");
 }
 
 void SkTraceRect(const SkRect& rect, const char* sz) {
     printf("SkRect %s ", sz);
     printf("x = %f ", SkScalarToDouble(rect.x()));
     printf("y = %f ", SkScalarToDouble(rect.y()));
     printf("w = %f ", SkScalarToDouble(rect.width()));
     printf("h = %f ", SkScalarToDouble(rect.height()));
     printf("\n");
 }
 #endif