Make SkSHA1 and SkM5 use common SkDigestHash result type

tests/BitmapHasherTest.cpp

Index: tests/BitmapHasherTest.cpp
===================================================================
--- tests/BitmapHasherTest.cpp	(revision 8685)
+++ tests/BitmapHasherTest.cpp	(working copy)
@@ -11,7 +11,7 @@
 #include "SkBitmapHasher.h"
 #include "SkColor.h"
 
-// Word size that is large enough to hold results of any checksum type.
+// Word size that is large enough to hold results of SkUInt64HashDigest.
 typedef uint64_t checksum_result;
 
 namespace skiatest {
@@ -38,7 +38,7 @@
         void RunTest() {
             // Test SkBitmapHasher
             SkBitmap bitmap;
-            SkHashDigest digest;
+            SkUInt64HashDigest digest;
             // initial test case
             CreateTestBitmap(bitmap, SkBitmap::kARGB_8888_Config, 333, 555, SK_ColorBLUE);
             REPORTER_ASSERT(fReporter, SkBitmapHasher::ComputeDigest(bitmap, &digest));