speed up benches: postpone hash computation in PictureRenderer.cpp

tools/PictureRenderer.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "PictureRenderer.h"
 #include "picture_utils.h"
 #include "SamplePipeControllers.h"
@@ skipping 280 matching lines @@
     canvas->readPixels(&bitmap, 0, 0);
     force_all_opaque(bitmap);
     BitmapAndDigest bitmapAndDigest(bitmap);
 
     SkString escapedInputFilename(inputFilename);
     replace_char(&escapedInputFilename, '.', '_');
 
     // TODO(epoger): what about including the config type within outputFilename?  That way,
     // we could combine results of different config types without conflicting filenames.
     SkString outputFilename;
-    const ImageDigest *imageDigestPtr = bitmapAndDigest.getImageDigestPtr();
     const char *outputSubdirPtr = NULL;
     if (useChecksumBasedFilenames) {
+        const ImageDigest *imageDigestPtr = bitmapAndDigest.getImageDigestPtr();
         outputSubdirPtr = escapedInputFilename.c_str();
         outputFilename.set(imageDigestPtr->getHashType());
         outputFilename.append("_");
         outputFilename.appendU64(imageDigestPtr->getHashValue());
     } else {
         outputFilename.set(escapedInputFilename);
         if (NULL != tileNumberPtr) {
             outputFilename.append("-tile");
             outputFilename.appendS32(*tileNumberPtr);
         }
@@ skipping 635 matching lines @@
     virtual SkString getConfigNameInternal() SK_OVERRIDE {
         return SkString("picture_clone");
     }
 };
 
 PictureRenderer* CreatePictureCloneRenderer() {
     return SkNEW(PictureCloneRenderer);
 }
 
 } // namespace sk_tools