GM: include filename extension (.png) of each output file in JSON summary

gm/gmmain.cpp

Index: gm/gmmain.cpp
===================================================================
--- gm/gmmain.cpp	(revision 9067)
+++ gm/gmmain.cpp	(working copy)
@@ -727,6 +727,7 @@
         }
         SkString completeNameString = baseNameString;
         completeNameString.append(renderModeDescriptor);
+        completeNameString.append(".png");
         const char* completeName = completeNameString.c_str();
 
         if (expectations.empty()) {
@@ -865,7 +866,9 @@
             if (!SkBitmapHasher::ComputeDigest(actualBitmap, &actualBitmapHash)) {
                 actualBitmapHash = 0;
             }
-            add_actual_results_to_json_summary(name.c_str(), actualBitmapHash,
+            SkString nameWithExtension(name);
+            nameWithExtension.append(".png");
+            add_actual_results_to_json_summary(nameWithExtension.c_str(), actualBitmapHash,
                                                ErrorCombination(kMissingExpectations_ErrorType),
                                                false);
             RecordTestResults(ErrorCombination(kMissingExpectations_ErrorType), name, "");