create sk_tools::Expectation class, similar to skiagm::Expectations class

tools/PictureRenderer.cpp

Index: tools/PictureRenderer.cpp
diff --git a/tools/PictureRenderer.cpp b/tools/PictureRenderer.cpp
index 7325c201b8ea2fd56acc0b82420fab265acdd2fd..ac639e59e8dfed46ca356d8dc3efa7d8db5f4148 100644
--- a/tools/PictureRenderer.cpp
+++ b/tools/PictureRenderer.cpp
@@ -297,7 +297,7 @@ static bool write(SkCanvas* canvas, const SkString& writePath, const SkString& m
     SkString outputFilename;
     const char *outputSubdirPtr = NULL;
     if (useChecksumBasedFilenames) {
-        const ImageDigest *imageDigestPtr = bitmapAndDigest.getImageDigestPtr();
+        ImageDigest *imageDigestPtr = bitmapAndDigest.getImageDigestPtr();
         outputSubdirPtr = escapedInputFilename.c_str();
         outputFilename.set(imageDigestPtr->getHashType());
         outputFilename.append("_");
@@ -312,7 +312,7 @@ static bool write(SkCanvas* canvas, const SkString& writePath, const SkString& m
     outputFilename.append(".png");
 
     if (NULL != jsonSummaryPtr) {
-        const ImageDigest *imageDigestPtr = bitmapAndDigest.getImageDigestPtr();
+        ImageDigest *imageDigestPtr = bitmapAndDigest.getImageDigestPtr();
         SkString outputRelativePath;
         if (outputSubdirPtr) {
             outputRelativePath.set(outputSubdirPtr);
@@ -325,8 +325,8 @@ static bool write(SkCanvas* canvas, const SkString& writePath, const SkString& m
         jsonSummaryPtr->add(inputFilename.c_str(), outputRelativePath.c_str(),
                             *imageDigestPtr, tileNumberPtr);
         if (!mismatchPath.isEmpty() &&
-            !jsonSummaryPtr->matchesExpectation(inputFilename.c_str(), *imageDigestPtr,
-                                                tileNumberPtr)) {
+            !jsonSummaryPtr->getExpectation(inputFilename.c_str(),
+                                            tileNumberPtr).matches(*imageDigestPtr)) {
             if (!write_bitmap_to_disk(bitmap, mismatchPath, outputSubdirPtr, outputFilename)) {
                 return false;
             }