Make SkSHA1 and SkM5 use common SkDigestHash result type

src/utils/SkBitmapHasher.cpp

Index: src/utils/SkBitmapHasher.cpp
===================================================================
--- src/utils/SkBitmapHasher.cpp	(revision 8685)
+++ src/utils/SkBitmapHasher.cpp	(working copy)
@@ -24,7 +24,7 @@
 }
 
 /*static*/ bool SkBitmapHasher::ComputeDigestInternal(
-        const SkBitmap& bitmap, const SkBitmapTransformer& transformer, SkHashDigest *result) {
+        const SkBitmap& bitmap, const SkBitmapTransformer& transformer, SkUInt64HashDigest *result) {
     size_t pixelBufferSize = transformer.bytesNeededTotal();
     size_t totalBufferSize = pixelBufferSize + 8; // leave room for x/y dimensions
 
@@ -45,7 +45,7 @@
     return true;
 }
 
-/*static*/ bool SkBitmapHasher::ComputeDigest(const SkBitmap& bitmap, SkHashDigest *result) {
+/*static*/ bool SkBitmapHasher::ComputeDigest(const SkBitmap& bitmap, SkUInt64HashDigest *result) {
     const SkBitmapTransformer::PixelFormat kPixelFormat =
         SkBitmapTransformer::kARGB_8888_Premul_PixelFormat;