Fix DMWriteTask to write PDF files correctly

dm/DMWriteTask.cpp

 #include "DMWriteTask.h"
 
 #include "DMUtil.h"
 #include "SkColorPriv.h"
 #include "SkCommonFlags.h"
 #include "SkData.h"
 #include "SkImageEncoder.h"
 #include "SkMD5.h"
 #include "SkMallocPixelRef.h"
 #include "SkOSFile.h"
@@ skipping 63 matching lines @@
     }
     return md5;
 }
 
 static SkString get_md5(const void* ptr, size_t len) {
     SkMD5 hasher;
     hasher.write(ptr, len);
     return get_md5_string(&hasher);
 }
 
+static bool write_asset(SkStreamAsset* input, SkWStream* output) {
+    return input->rewind() && output->writeStream(input, input->getLength());
+}
+
 static SkString get_md5(SkStreamAsset* stream) {
     SkMD5 hasher;
-    hasher.writeStream(stream, stream->getLength());
+    write_asset(stream, &hasher);
     return get_md5_string(&hasher);
 }
 
 struct JsonData {
     SkString name;            // E.g. "ninepatch-stretch", "desk-gws_skp"
     SkString config;          //      "gpu", "8888"
     SkString mode;            //      "direct", "default-tilegrid", "pipe"
     SkString sourceType;      //      "GM", "SKP"
     SkString md5;             // In ASCII, so 32 bytes long.
 };
@@ skipping 50 matching lines @@
         path.append(fExtension);
         // The path is unique, so two threads can't both write to the same file.
         // If already present we overwrite here, since the content may have changed.
     }
 
     SkFILEWStream file(path.c_str());
     if (!file.isValid()) {
         return this->fail("Can't open file.");
     }
 
-    bool ok = fData ? file.writeStream(fData, fData->getLength())
+    bool ok = fData ? write_asset(fData, &file)
                     : SkImageEncoder::EncodeStream(&file, fBitmap, SkImageEncoder::kPNG_Type, 100);
     if (!ok) {
         return this->fail("Can't write to file.");
     }
 }
 
 SkString WriteTask::name() const {
     SkString name("writing ");
     for (int i = 0; i < fSuffixes.count(); i++) {
         name.appendf("%s/", fSuffixes[i].c_str());
@@ skipping 34 matching lines @@
         }
     }
 
     SkString path = SkOSPath::Join(FLAGS_writePath[0], "dm.json");
     SkFILEWStream stream(path.c_str());
     stream.writeText(Json::StyledWriter().write(root).c_str());
     stream.flush();
 }
 
 }  // namespace DM