Make SkSHA1 and SkM5 use common SkDigestHash result type

src/utils/SkSHA1.cpp

Index: src/utils/SkSHA1.cpp
===================================================================
--- src/utils/SkSHA1.cpp	(revision 8685)
+++ src/utils/SkSHA1.cpp	(working copy)
@@ -58,7 +58,7 @@
     this->byteCount += inputLength;
 }
 
-void SkSHA1::finish(Digest& digest) {
+void SkSHA1::finish(SkHashDigest& digest) {
     // Get the number of bits before padding.
     uint8_t bits[8];
     encode(bits, this->byteCount << 3);
@@ -78,7 +78,17 @@
     this->update(bits, 8);
 
     // Write out digest.
-    encode(digest.data, this->state);
+    // TODO(epoger): eliminate the extra 20-byte copy, by writing directly into digest.data???
+    // NO, we can't do that, because digest.data is immutable (wrapped in SkData).
+    // Or:
+    //  1. malloc 20 bytes here (wrapped in an SkData object),
+    //  2. write the digest into the SkData-wrapped 20 bytes,
+    //  3. bump the ref counter on that SkData-wrapped 20 bytes,
+    //  4. replace digest's fSkDataPtr with the new one
+    size_t digestSize = 20;
+    uint8_t tempDigestData[digestSize];
+    encode(tempDigestData, this->state);
+    digest.copyFrom(tempDigestData, digestSize);
 
 #if defined(SK_SHA1_CLEAR_DATA)
     // Clear state.