[Zucchini] Format change: PatchElementHeader: Group fields by "old" and "new".

Previously PatchElementHeader members were ordered by:
  [old_offset, new_offset, old_length, new_length].
This CL changes the order to
  [old_offset, old_length, new_offset, new_length]
to be consistent with PatchHeader's grouping by "old" and "new".

Also improve comments in patch_read_write_unittest.cc, and fix
input value in PatchElementTest.WrongExtraData.

Change-Id: I0dab56b7de1ba99f0a2f686dfebdf422a9d1c3b0
Reviewed-on: https://chromium-review.googlesource.com/1043073
Commit-Queue: Samuel Huang <huangs@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556076}

components/zucchini/README.md

@@ -209,8 +209,8 @@ PatchElement self contained.
 Name | Format | Description
 --- | --- | ---
 old_offset | uint32 | Starting offset of the element in old file.
-new_offset | uint32 | Starting offset of the element in new file.
 old_length | uint32 | Length of the element in old file.
+new_offset | uint32 | Starting offset of the element in new file.
 new_length | uint32 | Length of the element in new file.
 exe_type | uint32 | Executable type for this unit, see `enum ExecutableType`.
 

components/zucchini/patch_reader.cc

@@ -38,8 +38,8 @@ bool ParseElementMatch(BufferSource* source, ElementMatch* element_match) {
   // Caveat: Element offsets and lengths can still be invalid (e.g., exceeding
   // archive bounds), but this will be checked later.
   element_match->old_element.offset = element_header.old_offset;
-  element_match->new_element.offset = element_header.new_offset;
   element_match->old_element.size = element_header.old_length;
+  element_match->new_element.offset = element_header.new_offset;
   element_match->new_element.size = element_header.new_length;
   element_match->old_element.exe_type = exe_type;
   element_match->new_element.exe_type = exe_type;

components/zucchini/patch_utils.h

@@ -34,20 +34,20 @@ struct PatchHeader {
 };
 
 // Sanity check.
-static_assert(sizeof(PatchHeader) == 20, "PatchHeader is 20 bytes");
+static_assert(sizeof(PatchHeader) == 20, "PatchHeader must be 20 bytes");
 
 // Header for a patch element, found at the beginning of every patch element.
 struct PatchElementHeader {
   uint32_t old_offset;
-  uint32_t new_offset;
   uint32_t old_length;
+  uint32_t new_offset;
   uint32_t new_length;
-  uint32_t exe_type;
+  uint32_t exe_type;  // ExecutableType.
 };
 
 // Sanity check.
 static_assert(sizeof(PatchElementHeader) == 20,
-              "PatchElementHeader is 28 bytes");
+              "PatchElementHeader must be 20 bytes");
 
 #pragma pack(pop)
 

components/zucchini/patch_writer.cc

@@ -23,10 +23,10 @@ bool SerializeElementMatch(const ElementMatch& element_match,
   PatchElementHeader element_header;
   element_header.old_offset =
       base::checked_cast<uint32_t>(element_match.old_element.offset);
-  element_header.new_offset =
-      base::checked_cast<uint32_t>(element_match.new_element.offset);
   element_header.old_length =
       base::checked_cast<uint32_t>(element_match.old_element.size);
+  element_header.new_offset =
+      base::checked_cast<uint32_t>(element_match.new_element.offset);
   element_header.new_length =
       base::checked_cast<uint32_t>(element_match.new_element.size);
   element_header.exe_type = element_match.exe_type();