Switch FileWriter::Write to boolean result code.

FileWriter::Write returned either the number of bytes written, or a negative
error code. No clients were doing anything with the result other than checking
for success or failure, and many clients were considering any non-zero result
success.

So, I changed the API to return less information, but just the information the
clients needed. Success or failure.

BUG=chromium-os:8521
TEST=Unittests

Change-Id: I51513d6aa7b704dc27fb90d5fae4dc7118a3f86c
Reviewed-on: https://gerrit.chromium.org/gerrit/11532
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Commit-Ready: Don Garrett <dgarrett@chromium.org>
diff --git a/delta_diff_generator.cc b/delta_diff_generator.cc
index 1c962f1..cc8f352 100644
--- a/delta_diff_generator.cc
+++ b/delta_diff_generator.cc
@@ -337,8 +337,7 @@
 // Returns true on success.
 bool WriteUint64AsBigEndian(FileWriter* writer, const uint64_t value) {
   uint64_t value_be = htobe64(value);
-  TEST_AND_RETURN_FALSE(writer->Write(&value_be, sizeof(value_be)) ==
-                        sizeof(value_be));
+  TEST_AND_RETURN_FALSE(writer->Write(&value_be, sizeof(value_be)));
   return true;
 }
 
@@ -1163,8 +1162,7 @@
     TEST_AND_RETURN_FALSE(rc == static_cast<ssize_t>(buf.size()));
 
     op->set_data_offset(out_file_size);
-    TEST_AND_RETURN_FALSE(writer.Write(&buf[0], buf.size()) ==
-                          static_cast<ssize_t>(buf.size()));
+    TEST_AND_RETURN_FALSE(writer.Write(&buf[0], buf.size()));
     out_file_size += buf.size();
   }
   return true;
@@ -1486,8 +1484,7 @@
   ScopedFileWriterCloser writer_closer(&writer);
 
   // Write header
-  TEST_AND_RETURN_FALSE(writer.Write(kDeltaMagic, strlen(kDeltaMagic)) ==
-                        static_cast<ssize_t>(strlen(kDeltaMagic)));
+  TEST_AND_RETURN_FALSE(writer.Write(kDeltaMagic, strlen(kDeltaMagic)));
 
   // Write version number
   TEST_AND_RETURN_FALSE(WriteUint64AsBigEndian(&writer, kVersionNumber));
@@ -1500,8 +1497,7 @@
   LOG(INFO) << "Writing final delta file protobuf... "
             << serialized_manifest.size();
   TEST_AND_RETURN_FALSE(writer.Write(serialized_manifest.data(),
-                                     serialized_manifest.size()) ==
-                        static_cast<ssize_t>(serialized_manifest.size()));
+                                     serialized_manifest.size()));
 
   // Append the data blobs
   LOG(INFO) << "Writing final delta file data blobs...";
@@ -1516,7 +1512,7 @@
       break;
     }
     TEST_AND_RETURN_FALSE_ERRNO(rc > 0);
-    TEST_AND_RETURN_FALSE(writer.Write(buf, rc) == rc);
+    TEST_AND_RETURN_FALSE(writer.Write(buf, rc));
   }
 
   // Write signature blob.
@@ -1528,8 +1524,7 @@
         vector<string>(1, private_key_path),
         &signature_blob));
     TEST_AND_RETURN_FALSE(writer.Write(&signature_blob[0],
-                                       signature_blob.size()) ==
-                          static_cast<ssize_t>(signature_blob.size()));
+                                       signature_blob.size()));
   }
 
   int64_t manifest_metadata_size =