Make SkSHA1 and SkM5 use common SkDigestHash result type

gm/gmmain.cpp

Index: gm/gmmain.cpp
===================================================================
--- gm/gmmain.cpp	(revision 8685)
+++ gm/gmmain.cpp	(working copy)
@@ -714,11 +714,10 @@
                                              const char renderModeDescriptor[],
                                              bool addToJsonSummary) {
         ErrorCombination errors;
-        SkHashDigest actualBitmapHash;
-        // TODO(epoger): Better handling for error returned by ComputeDigest()?
-        // For now, we just report a digest of 0 in error cases, like before.
+        BITMAP_HASH_TYPE actualBitmapHash;
         if (!SkBitmapHasher::ComputeDigest(actualBitmap, &actualBitmapHash)) {
-            actualBitmapHash = 0;
+            // TODO(epoger): Better handling for error returned by ComputeDigest()?
+            // For now, we just leave actualBitmapHash empty.
         }
         SkString completeNameString = baseNameString;
         completeNameString.append(renderModeDescriptor);
@@ -768,7 +767,7 @@
      * depending on status.
      */
     void add_actual_results_to_json_summary(const char testName[],
-                                            const SkHashDigest& actualBitmapHash,
+                                            const BITMAP_HASH_TYPE& actualBitmapHash,
                                             ErrorCombination result,
                                             bool ignoreFailure) {
         Json::Value actualResults;
@@ -864,11 +863,10 @@
         } else {
             // If we are running without expectations, we still want to
             // record the actual results.
-            SkHashDigest actualBitmapHash;
-            // TODO(epoger): Better handling for error returned by ComputeDigest()?
-            // For now, we just report a digest of 0 in error cases, like before.
+            BITMAP_HASH_TYPE actualBitmapHash;
             if (!SkBitmapHasher::ComputeDigest(actualBitmap, &actualBitmapHash)) {
-                actualBitmapHash = 0;
+                // TODO(epoger): Better handling for error returned by ComputeDigest()?
+                // For now, we just leave actualBitmapHash empty.
             }
             add_actual_results_to_json_summary(name.c_str(), actualBitmapHash,
                                                ErrorCombination(kMissingExpectations_ErrorType),