skimage: report failure if expectation not found.

If the expectation file exists, but the particular file being
decoded has no expectation, report a failure.

This is more appropriate since the intended use is that an
expectation will be created for each file. Without an expectation,
we cannot know whether the decoder has changed.

R=epoger@google.com

Review URL: https://codereview.chromium.org/15094011

git-svn-id: http://skia.googlecode.com/svn/trunk@9122 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skimage_main.cpp b/tools/skimage_main.cpp
index 2041f7b..e434ff0 100644
--- a/tools/skimage_main.cpp
+++ b/tools/skimage_main.cpp
@@ -202,9 +202,13 @@
  *  Compare against an expectation for this filename, if there is one.
  *  @param bitmap SkBitmap to compare to the expected value.
  *  @param filename String used to find the expected value.
- *  @return bool True if the bitmap matched the expectation, or if there was no expectation. False
- *      if there was an expecation that the bitmap did not match, or if an expectation could not be
- *      computed from an expectation.
+ *  @return bool True in any of these cases:
+ *                  - the bitmap matches the expectation.
+ *                  - there is no expectations file.
+ *               False in any of these cases:
+ *                  - there is an expectations file, but no expectation for this bitmap.
+ *                  - there is an expectation for this bitmap, but it did not match.
+ *                  - expectation could not be computed from the bitmap.
  */
 static bool compare_to_expectations_if_necessary(const SkBitmap& bitmap, const char* filename,
                                                  SkTArray<SkString, false>* failureArray) {
@@ -214,7 +218,11 @@
 
     skiagm::Expectations jsExpectation = gJsonExpectations->get(filename);
     if (jsExpectation.empty()) {
-        return true;
+        if (failureArray != NULL) {
+            failureArray->push_back().printf("decoded %s, but could not find expectation.",
+                                             filename);
+        }
+        return false;
     }
 
     SkHashDigest checksum;