Make SkSHA1 and SkM5 use common SkDigestHash result type

src/utils/SkMD5.cpp

Index: src/utils/SkMD5.cpp
===================================================================
--- src/utils/SkMD5.cpp	(revision 8685)
+++ src/utils/SkMD5.cpp	(working copy)
@@ -60,7 +60,7 @@
     this->byteCount += inputLength;
 }
 
-void SkMD5::finish(Digest& digest) {
+void SkMD5::finish(SkHashDigest& digest) {
     // Get the number of bits before padding.
     uint8_t bits[8];
     encode(bits, this->byteCount << 3);
@@ -80,7 +80,17 @@
     this->update(bits, 8);
 
     // Write out digest.
-    encode(digest.data, this->state);
+    // TODO(epoger): eliminate the extra 16-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 16 bytes here (wrapped in an SkData object),
+    //  2. write the digest into the SkData-wrapped 16 bytes,
+    //  3. bump the ref counter on that SkData-wrapped 16 bytes,
+    //  4. replace digest's fSkDataPtr with the new one
+    size_t digestSize = 16;
+    uint8_t tempDigestData[digestSize];
+    encode(tempDigestData, this->state);
+    digest.copyFrom(tempDigestData, digestSize);
 
 #if defined(SK_MD5_CLEAR_DATA)
     // Clear state.
@@ -90,12 +100,12 @@
 
 struct F { uint32_t operator()(uint32_t x, uint32_t y, uint32_t z) {
     //return (x & y) | ((~x) & z);
-    return ((y ^ z) & x) ^ z; //equivelent but faster
+    return ((y ^ z) & x) ^ z; //equivalent but faster
 }};
 
 struct G { uint32_t operator()(uint32_t x, uint32_t y, uint32_t z) {
     return (x & z) | (y & (~z));
-    //return ((x ^ y) & z) ^ y; //equivelent but slower
+    //return ((x ^ y) & z) ^ y; //equivalent but slower
 }};
 
 struct H { uint32_t operator()(uint32_t x, uint32_t y, uint32_t z) {