pdfviewer: more code comments + concat the pdf matrix with the existing matrix in canvas, instead o…

experimental/PdfViewer/SkPdfUtils.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPdfUtils_DEFINED
 #define SkPdfUtils_DEFINED
 
@@ skipping 12 matching lines @@
     kOK_SkPdfResult,
     kPartial_SkPdfResult,
     kNYI_SkPdfResult,
     kIgnoreError_SkPdfResult,
     kError_SkPdfResult,
     kUnsupported_SkPdfResult,
 
     kCount_SkPdfResult
 };
 
+// In order to operate fast, when we parse the pdf, we try not to allocate many new strings,
+// and if possible we refer the string in the pdf stream.
 struct NotOwnedString {
     const unsigned char* fBuffer;
     // TODO(edisonn): clean up, the last two bytes are used to signal if compression is used
     size_t fBytes;
 
     static void init(NotOwnedString* str) {
         str->fBuffer = NULL;
         str->fBytes = 0;
     }
 
@@ skipping 67 matching lines @@
 
 #else
 #define TRACE_COMMENT(ch)
 #define TRACE_TK(ch)
 #define TRACE_NAME(start,end)
 #define TRACE_STRING(start,end)
 #define TRACE_HEXSTRING(start,end)
 #endif
 
 #endif   // SkPdfUtils_DEFINED