Add size_t bytesWritten() const to SkWStream.

BUG=skia:
R=reed@google.com, mtklein@google.com, robertphillips@google.com, bungeman@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/187653003

git-svn-id: http://skia.googlecode.com/svn/trunk@13684 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkMD5.h b/src/utils/SkMD5.h
index 0148641..4f50478 100644
--- a/src/utils/SkMD5.h
+++ b/src/utils/SkMD5.h
@@ -29,6 +29,8 @@
         return true;
     }
 
+    virtual size_t bytesWritten() const SK_OVERRIDE { return SkToSizeT(this->byteCount); }
+
     /** Processes input, adding it to the digest. Calling this after finish is undefined. */
     void update(const uint8_t* input, size_t length);