Revert of [Sync] Add size and crc32c to AttachmentId. (patchset #8 id:140001 of https://codereview.chromium.org/982883002/)

Reason for revert:
Broke build on iOS_Device

http://build.chromium.org/p/chromium.mac/builders/iOS_Device/builds/26684/steps/compile/logs/stdio

Undefined symbols for architecture armv7:
  "syncer::Attachment::CreateFromParts(syncer::AttachmentId const&, scoped_refptr<base::RefCountedMemory> const&, unsigned int)", referenced from:
      syncer::(anonymous namespace)::MockAttachmentStore::RespondToRead(std::__1::set<syncer::AttachmentId, std::__1::less<syncer::AttachmentId>, std::__1::allocator<syncer::AttachmentId> > const&) in attachment_service_impl_unittest.o
      syncer::(anonymous namespace)::MockAttachmentDownloader::RespondToDownload(syncer::AttachmentId const&, syncer::AttachmentDownloader::DownloadResult const&) in attachment_service_impl_unittest.o
      syncer::gtest_case_AttachmentStoreTest_::Write_NoOverwriteNoError<syncer::InMemoryAttachmentStoreFactory>::TestBody() in in_memory_attachment_store_unittest.o
      syncer::OnDiskAttachmentStoreSpecificTest_MismatchedCrc_Test::TestBody() in on_disk_attachment_store_unittest.o
      syncer::gtest_case_AttachmentStoreTest_::Write_NoOverwriteNoError<syncer::OnDiskAttachmentStoreFactory>::TestBody() in on_disk_attachment_store_unittest.o
  "syncer::CreateAttachmentIdProto()", referenced from:
      syncer::AddAttachment(sync_pb::AttachmentMetadata*, bool) in directory_commit_contribution_unittest.o
      syncer::DirectoryUpdateHandlerProcessUpdateTest_ProcessAndApplyUpdatesWithAttachments_Test::TestBody() in directory_update_handler_unittest.o
      syncer::DirectoryUpdateHandlerApplyUpdateTest_SimpleConflictDifferentAttachmentMetadata_Test::TestBody() in directory_update_handler_unittest.o
      syncer::DirectoryUpdateHandlerApplyUpdateTest_SimpleConflictSameAttachmentMetadataDifferentOrder_Test::TestBody() in directory_update_handler_unittest.o
      syncer::AttachmentIdProtoTest_UniqueIdFormat_Test::TestBody() in attachment_id_proto_unittest.o
      syncer::AttachmentIdProtoTest_CreateAttachmentMetadata_NonEmpty_Test::TestBody() in attachment_id_proto_unittest.o
      syncer::SyncManagerChangeProcessingTest_AttachmentMetadataOnlyChanges_Test::TestBody() in sync_manager_impl_unittest.o
      ...
  "syncer::AttachmentId::Create()", referenced from:
      syncer::(anonymous namespace)::SyncDataTest_CreateLocalDataWithAttachments_Test::TestBody() in sync_data_unittest.o
      syncer::AttachmentDownloaderImplTest_HappyCase_Test::TestBody() in attachment_downloader_impl_unittest.o
      syncer::AttachmentDownloaderImplTest_SameIdMultipleDownloads_Test::TestBody() in attachment_downloader_impl_unittest.o
      syncer::AttachmentDownloaderImplTest_RequestAccessTokenFails_Test::TestBody() in attachment_downloader_impl_unittest.o
      syncer::AttachmentDownloaderImplTest_URLFetcher_BadToken_Test::TestBody() in attachment_downloader_impl_unittest.o
      syncer::AttachmentDownloaderImplTest_URLFetcher_ServiceUnavailable_Test::TestBody() in attachment_downloader_impl_unittest.o
      syncer::AttachmentDownloaderImplTest_NoHash_Test::TestBody() in attachment_downloader_impl_unittest.o
      ...
ld: symbol(s) not found for architecture armv7
clang:error: linker command failed with exit code 1 (use -v to see invocation)

Original issue's description:
> [Sync] Add size and crc32c to AttachmentId.
>
> The purpose of this change is to ensure that if a client knows about an
> attachment (i.e. has an AttachmentId or AttachmentIdProto) it will know
> the attachment's size even if the attachment has never been available on
> the local device.
>
> The idea is that by storing size locally, we can simplify remote storage
> management.
>
> Move crc32c out of Attachment now that it's part of AttachmentId.
>
> BUG=464431
>
> Committed: https://crrev.com/23ae3128db0d84a6b1ffa640568a5ec90cfc8808
> Cr-Commit-Position: refs/heads/master@{#319794}

TBR=pavely@chromium.org,maniscalco@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=464431

Review URL: https://codereview.chromium.org/995683002

Cr-Commit-Position: refs/heads/master@{#319807}

27 files changed, 115 insertions, 215 deletions

diff --git a/sync/api/attachments/attachment.cc b/sync/api/attachments/attachment.cc
index 32a514a..b682520 100644
--- a/sync/api/attachments/attachment.cc
+++ b/sync/api/attachments/attachment.cc
@@ -15,14 +15,15 @@ Attachment::~Attachment() {}
 Attachment Attachment::Create(
     const scoped_refptr<base::RefCountedMemory>& data) {
   uint32_t crc32c = ComputeCrc32c(data);
-  return CreateFromParts(AttachmentId::Create(data->size(), crc32c), data);
+  return CreateFromParts(AttachmentId::Create(), data, crc32c);
 }
 
 // Static.
 Attachment Attachment::CreateFromParts(
     const AttachmentId& id,
-    const scoped_refptr<base::RefCountedMemory>& data) {
-  return Attachment(id, data);
+    const scoped_refptr<base::RefCountedMemory>& data,
+    uint32_t crc32c) {
+  return Attachment(id, data, crc32c);
 }
 
 const AttachmentId& Attachment::GetId() const { return id_; }
@@ -31,14 +32,12 @@ const scoped_refptr<base::RefCountedMemory>& Attachment::GetData() const {
   return data_;
 }
 
-uint32_t Attachment::GetCrc32c() const {
-  return id_.GetCrc32c();
-}
+uint32_t Attachment::GetCrc32c() const { return crc32c_; }
 
 Attachment::Attachment(const AttachmentId& id,
-                       const scoped_refptr<base::RefCountedMemory>& data)
-    : id_(id), data_(data) {
-  DCHECK_EQ(id.GetSize(), data->size());
+                       const scoped_refptr<base::RefCountedMemory>& data,
+                       uint32_t crc32c)
+    : id_(id), data_(data), crc32c_(crc32c) {
   DCHECK(data.get());
 }
 
diff --git a/sync/api/attachments/attachment.h b/sync/api/attachments/attachment.h
index 7999269..51fe986 100644
--- a/sync/api/attachments/attachment.h
+++ b/sync/api/attachments/attachment.h
@@ -34,13 +34,14 @@ class SYNC_EXPORT Attachment {
   // Used when creating a brand new attachment.
   static Attachment Create(const scoped_refptr<base::RefCountedMemory>& data);
 
-  // Creates an attachment with the supplied id and data.
+  // Creates an attachment with the supplied id, data and crc32c.
   //
   // Used when you want to recreate a specific attachment. E.g. creating a local
   // copy of an attachment that already exists on the sync server.
   static Attachment CreateFromParts(
       const AttachmentId& id,
-      const scoped_refptr<base::RefCountedMemory>& data);
+      const scoped_refptr<base::RefCountedMemory>& data,
+      uint32_t crc32c);
 
   // Returns this attachment's id.
   const AttachmentId& GetId() const;
@@ -57,9 +58,11 @@ class SYNC_EXPORT Attachment {
  private:
   AttachmentId id_;
   scoped_refptr<base::RefCountedMemory> data_;
+  uint32_t crc32c_;
 
   Attachment(const AttachmentId& id,
-             const scoped_refptr<base::RefCountedMemory>& data);
+             const scoped_refptr<base::RefCountedMemory>& data,
+             uint32_t crc32c);
 };
 
 typedef std::vector<syncer::Attachment> AttachmentList;
diff --git a/sync/api/attachments/attachment_id.cc b/sync/api/attachments/attachment_id.cc
index 07f3410..e61705e 100644
--- a/sync/api/attachments/attachment_id.cc
+++ b/sync/api/attachments/attachment_id.cc
@@ -52,8 +52,8 @@ bool AttachmentId::operator<(const AttachmentId& other) const {
 }
 
 // Static.
-AttachmentId AttachmentId::Create(size_t size, uint32_t crc32c) {
-  sync_pb::AttachmentIdProto proto = CreateAttachmentIdProto(size, crc32c);
+AttachmentId AttachmentId::Create() {
+  sync_pb::AttachmentIdProto proto = CreateAttachmentIdProto();
   return AttachmentId(&proto);
 }
 
@@ -71,12 +71,4 @@ const sync_pb::AttachmentIdProto& AttachmentId::GetProto() const {
 AttachmentId::AttachmentId(sync_pb::AttachmentIdProto* proto)
     : proto_(proto) {}
 
-size_t AttachmentId::GetSize() const {
-  return proto_.Get().size_bytes();
-}
-
-uint32_t AttachmentId::GetCrc32c() const {
-  return proto_.Get().crc32c();
-}
-
 }  // namespace syncer
diff --git a/sync/api/attachments/attachment_id.h b/sync/api/attachments/attachment_id.h
index 1c53355..6ce331a 100644
--- a/sync/api/attachments/attachment_id.h
+++ b/sync/api/attachments/attachment_id.h
@@ -35,24 +35,14 @@ class SYNC_EXPORT AttachmentId {
   // Needed for using AttachmentId as key in std::map.
   bool operator<(const AttachmentId& other) const;
 
-  // Creates a unique id for an attachment.
-  //
-  // |size| is the attachment's size in bytes.
-  //
-  // |crc32c| is the attachment's crc32c.
-  static AttachmentId Create(size_t size, uint32_t crc32c);
+  // Creates a unique attachment id.
+  static AttachmentId Create();
 
   // Creates an attachment id from an initialized proto.
   static AttachmentId CreateFromProto(const sync_pb::AttachmentIdProto& proto);
 
   const sync_pb::AttachmentIdProto& GetProto() const;
 
-  // Returns the size (in bytes) the attachment.
-  size_t GetSize() const;
-
-  // Returns the crc32c the attachment.
-  uint32_t GetCrc32c() const;
-
  private:
   // Necessary since we forward-declare sync_pb::AttachmentIdProto; see comments
   // in immutable.h.
diff --git a/sync/api/attachments/attachment_id_unittest.cc b/sync/api/attachments/attachment_id_unittest.cc
index dae5182..3e6bb0a 100644
--- a/sync/api/attachments/attachment_id_unittest.cc
+++ b/sync/api/attachments/attachment_id_unittest.cc
@@ -10,25 +10,29 @@
 
 namespace syncer {
 
+namespace {
+
+}  // namespace
+
 class AttachmentIdTest : public testing::Test {};
 
 TEST_F(AttachmentIdTest, Create_IsUnique) {
-  AttachmentId id1 = AttachmentId::Create(0, 0);
-  AttachmentId id2 = AttachmentId::Create(0, 0);
+  AttachmentId id1 = AttachmentId::Create();
+  AttachmentId id2 = AttachmentId::Create();
   EXPECT_NE(id1, id2);
 }
 
 TEST_F(AttachmentIdTest, OperatorEqual) {
-  AttachmentId id1 = AttachmentId::Create(0, 0);
+  AttachmentId id1 = AttachmentId::Create();
   AttachmentId id2(id1);
   EXPECT_EQ(id1, id2);
 }
 
 TEST_F(AttachmentIdTest, OperatorLess) {
-  AttachmentId id1 = AttachmentId::Create(0, 0);
+  AttachmentId id1 = AttachmentId::Create();
   EXPECT_FALSE(id1 < id1);
 
-  AttachmentId id2 = AttachmentId::Create(0, 0);
+  AttachmentId id2 = AttachmentId::Create();
   EXPECT_FALSE(id1 < id1);
 
   EXPECT_NE(id1, id2);
diff --git a/sync/api/attachments/attachment_metadata.h b/sync/api/attachments/attachment_metadata.h
index 6eef6c6..10761f8 100644
--- a/sync/api/attachments/attachment_metadata.h
+++ b/sync/api/attachments/attachment_metadata.h
@@ -30,9 +30,6 @@ class SYNC_EXPORT AttachmentMetadata {
   size_t GetSize() const;
 
  private:
-  // TODO(maniscalco): Reconcile AttachmentMetadata and
-  // AttachmentId. AttachmentId knows the size of the attachment so
-  // AttachmentMetadata may not be necessary (crbug/465375).
   AttachmentId id_;
   size_t size_;
 };
diff --git a/sync/api/attachments/attachment_metadata_unittest.cc b/sync/api/attachments/attachment_metadata_unittest.cc
index a736b7e..06477d0 100644
--- a/sync/api/attachments/attachment_metadata_unittest.cc
+++ b/sync/api/attachments/attachment_metadata_unittest.cc
@@ -11,9 +11,8 @@ namespace syncer {
 class AttachmentMetadataTest : public testing::Test {};
 
 TEST_F(AttachmentMetadataTest, Create) {
+  AttachmentId id = AttachmentId::Create();
   size_t size = 42;
-  uint32_t crc32c = 2349829;
-  AttachmentId id = AttachmentId::Create(size, crc32c);
   AttachmentMetadata metadata(id, size);
   EXPECT_EQ(metadata.GetId(), id);
   EXPECT_EQ(metadata.GetSize(), size);
diff --git a/sync/api/attachments/attachment_unittest.cc b/sync/api/attachments/attachment_unittest.cc
index cd1e3e4..49b4cab 100644
--- a/sync/api/attachments/attachment_unittest.cc
+++ b/sync/api/attachments/attachment_unittest.cc
@@ -38,11 +38,11 @@ TEST_F(AttachmentTest, Create_WithEmptyData) {
 }
 
 TEST_F(AttachmentTest, CreateFromParts_HappyCase) {
+  AttachmentId id = AttachmentId::Create();
   scoped_refptr<base::RefCountedString> some_data(new base::RefCountedString);
   some_data->data() = kAttachmentData;
   uint32_t crc32c = ComputeCrc32c(some_data);
-  AttachmentId id = AttachmentId::Create(some_data->size(), crc32c);
-  Attachment a = Attachment::CreateFromParts(id, some_data);
+  Attachment a = Attachment::CreateFromParts(id, some_data, crc32c);
   EXPECT_EQ(id, a.GetId());
   EXPECT_EQ(some_data, a.GetData());
 }
diff --git a/sync/api/sync_data_unittest.cc b/sync/api/sync_data_unittest.cc
index 9d45149..94c3f4c 100644
--- a/sync/api/sync_data_unittest.cc
+++ b/sync/api/sync_data_unittest.cc
@@ -72,9 +72,9 @@ TEST_F(SyncDataTest, CreateLocalData) {
 TEST_F(SyncDataTest, CreateLocalDataWithAttachments) {
   specifics.mutable_preference();
   AttachmentIdList attachment_ids;
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
+  attachment_ids.push_back(AttachmentId::Create());
+  attachment_ids.push_back(AttachmentId::Create());
+  attachment_ids.push_back(AttachmentId::Create());
 
   SyncData data = SyncData::CreateLocalDataWithAttachments(
       kSyncTag, kNonUniqueTitle, specifics, attachment_ids);
diff --git a/sync/engine/directory_commit_contribution_unittest.cc b/sync/engine/directory_commit_contribution_unittest.cc
index 720f088..b5612b6 100644
--- a/sync/engine/directory_commit_contribution_unittest.cc
+++ b/sync/engine/directory_commit_contribution_unittest.cc
@@ -350,7 +350,7 @@ TEST_F(DirectoryCommitContributionTest, HierarchySupport_Preferences) {
 
 void AddAttachment(sync_pb::AttachmentMetadata* metadata, bool is_on_server) {
   sync_pb::AttachmentMetadataRecord record;
-  *record.mutable_id() = CreateAttachmentIdProto(0, 0);
+  *record.mutable_id() = CreateAttachmentIdProto();
   record.set_is_on_server(is_on_server);
   *metadata->add_record() = record;
 }
diff --git a/sync/engine/directory_update_handler_unittest.cc b/sync/engine/directory_update_handler_unittest.cc
index 2311d0f..46e2860 100644
--- a/sync/engine/directory_update_handler_unittest.cc
+++ b/sync/engine/directory_update_handler_unittest.cc
@@ -401,7 +401,7 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest,
   scoped_ptr<sync_pb::SyncEntity> e1 = CreateUpdate(
       SyncableIdToProto(Id::CreateFromServerId("e1")), "", ARTICLES);
   sync_pb::AttachmentIdProto* attachment_id = e1->add_attachment_id();
-  *attachment_id = CreateAttachmentIdProto(0, 0);
+  *attachment_id = CreateAttachmentIdProto();
 
   SyncEntityList updates;
   updates.push_back(e1.get());
@@ -1080,10 +1080,8 @@ TEST_F(DirectoryUpdateHandlerApplyUpdateTest,
   *specifics.mutable_article() = sync_pb::ArticleSpecifics();
   int64 handle = entry_factory()->CreateSyncedItem("art1", ARTICLES, is_folder);
 
-  sync_pb::AttachmentIdProto local_attachment_id =
-      CreateAttachmentIdProto(0, 0);
-  sync_pb::AttachmentIdProto server_attachment_id =
-      CreateAttachmentIdProto(0, 0);
+  sync_pb::AttachmentIdProto local_attachment_id = CreateAttachmentIdProto();
+  sync_pb::AttachmentIdProto server_attachment_id = CreateAttachmentIdProto();
 
   // Add an attachment to the local attachment metadata.
   sync_pb::AttachmentMetadata local_metadata;
@@ -1124,8 +1122,8 @@ TEST_F(DirectoryUpdateHandlerApplyUpdateTest,
   *specifics.mutable_article() = sync_pb::ArticleSpecifics();
   int64 handle = entry_factory()->CreateSyncedItem("art1", ARTICLES, is_folder);
 
-  sync_pb::AttachmentIdProto id1 = CreateAttachmentIdProto(0, 0);
-  sync_pb::AttachmentIdProto id2 = CreateAttachmentIdProto(0, 0);
+  sync_pb::AttachmentIdProto id1 = CreateAttachmentIdProto();
+  sync_pb::AttachmentIdProto id2 = CreateAttachmentIdProto();
 
   // Add id1, then id2 to the local attachment metadata.
   sync_pb::AttachmentMetadata local_metadata;
diff --git a/sync/internal_api/attachments/attachment_downloader_impl.cc b/sync/internal_api/attachments/attachment_downloader_impl.cc
index f2e6a00..56a2c34 100644
--- a/sync/internal_api/attachments/attachment_downloader_impl.cc
+++ b/sync/internal_api/attachments/attachment_downloader_impl.cc
@@ -132,7 +132,7 @@ void AttachmentDownloaderImpl::OnGetTokenFailure(
     DownloadState* download_state = *iter;
     scoped_refptr<base::RefCountedString> null_attachment_data;
     ReportResult(*download_state, DOWNLOAD_TRANSIENT_ERROR,
-                 null_attachment_data);
+                 null_attachment_data, 0);
     DCHECK(state_map_.find(download_state->attachment_url) != state_map_.end());
     state_map_.erase(download_state->attachment_url);
   }
@@ -175,13 +175,7 @@ void AttachmentDownloaderImpl::OnURLFetchComplete(
       // locally calculated one will be stored and used for further checks.
       result = DOWNLOAD_TRANSIENT_ERROR;
     } else {
-      // If the id's crc32c doesn't match that of the downloaded attachment,
-      // then we're stuck and retrying is unlikely to help.
-      if (attachment_crc32c != download_state.attachment_id.GetCrc32c()) {
-        result = DOWNLOAD_UNSPECIFIED_ERROR;
-      } else {
-        result = DOWNLOAD_SUCCESS;
-      }
+      result = DOWNLOAD_SUCCESS;
     }
     UMA_HISTOGRAM_BOOLEAN("Sync.Attachments.DownloadChecksumResult",
                           result == DOWNLOAD_SUCCESS);
@@ -199,7 +193,7 @@ void AttachmentDownloaderImpl::OnURLFetchComplete(
   } else if (response_code == net::URLFetcher::RESPONSE_CODE_INVALID) {
     result = DOWNLOAD_TRANSIENT_ERROR;
   }
-  ReportResult(download_state, result, attachment_data);
+  ReportResult(download_state, result, attachment_data, attachment_crc32c);
   state_map_.erase(iter);
 }
 
@@ -227,7 +221,8 @@ void AttachmentDownloaderImpl::RequestAccessToken(
 void AttachmentDownloaderImpl::ReportResult(
     const DownloadState& download_state,
     const DownloadResult& result,
-    const scoped_refptr<base::RefCountedString>& attachment_data) {
+    const scoped_refptr<base::RefCountedString>& attachment_data,
+    uint32_t attachment_crc32c) {
   std::vector<DownloadCallback>::const_iterator iter;
   for (iter = download_state.user_callbacks.begin();
        iter != download_state.user_callbacks.end();
@@ -235,7 +230,7 @@ void AttachmentDownloaderImpl::ReportResult(
     scoped_ptr<Attachment> attachment;
     if (result == DOWNLOAD_SUCCESS) {
       attachment.reset(new Attachment(Attachment::CreateFromParts(
-          download_state.attachment_id, attachment_data)));
+          download_state.attachment_id, attachment_data, attachment_crc32c)));
     }
 
     base::MessageLoop::current()->PostTask(
diff --git a/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc b/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
index 0cae099..1d026eb 100644
--- a/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
+++ b/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
@@ -152,12 +152,7 @@ class AttachmentDownloaderImplTest : public testing::Test {
     HASH_HEADER_INVALID
   };
 
-  AttachmentDownloaderImplTest()
-      : num_completed_downloads_(0),
-        attachment_id_(
-            Attachment::Create(new base::RefCountedStaticMemory(
-                                   kAttachmentContent,
-                                   strlen(kAttachmentContent))).GetId()) {}
+  AttachmentDownloaderImplTest() : num_completed_downloads_(0) {}
 
   void SetUp() override;
   void TearDown() override;
@@ -168,8 +163,6 @@ class AttachmentDownloaderImplTest : public testing::Test {
 
   int num_completed_downloads() { return num_completed_downloads_; }
 
-  const AttachmentId attachment_id() const { return attachment_id_; }
-
   AttachmentDownloader::DownloadCallback download_callback(
       const AttachmentId& id) {
     return base::Bind(&AttachmentDownloaderImplTest::DownloadDone,
@@ -200,7 +193,6 @@ class AttachmentDownloaderImplTest : public testing::Test {
   scoped_ptr<AttachmentDownloader> attachment_downloader_;
   ResultsMap download_results_;
   int num_completed_downloads_;
-  const AttachmentId attachment_id_;
 };
 
 void AttachmentDownloaderImplTest::SetUp() {
@@ -302,7 +294,7 @@ void AttachmentDownloaderImplTest::AddHashHeader(
 }
 
 TEST_F(AttachmentDownloaderImplTest, HappyCase) {
-  AttachmentId id1 = attachment_id();
+  AttachmentId id1 = AttachmentId::Create();
   // DownloadAttachment should trigger RequestAccessToken.
   downloader()->DownloadAttachment(id1, download_callback(id1));
   RunMessageLoop();
@@ -322,7 +314,7 @@ TEST_F(AttachmentDownloaderImplTest, HappyCase) {
 }
 
 TEST_F(AttachmentDownloaderImplTest, SameIdMultipleDownloads) {
-  AttachmentId id1 = attachment_id();
+  AttachmentId id1 = AttachmentId::Create();
   base::HistogramTester histogram_tester;
   // Call DownloadAttachment two times for the same id.
   downloader()->DownloadAttachment(id1, download_callback(id1));
@@ -359,8 +351,8 @@ TEST_F(AttachmentDownloaderImplTest, SameIdMultipleDownloads) {
 }
 
 TEST_F(AttachmentDownloaderImplTest, RequestAccessTokenFails) {
-  AttachmentId id1 = attachment_id();
-  AttachmentId id2 = AttachmentId::Create(id1.GetSize(), id1.GetCrc32c());
+  AttachmentId id1 = AttachmentId::Create();
+  AttachmentId id2 = AttachmentId::Create();
   // Trigger first RequestAccessToken.
   downloader()->DownloadAttachment(id1, download_callback(id1));
   RunMessageLoop();
@@ -383,7 +375,7 @@ TEST_F(AttachmentDownloaderImplTest, RequestAccessTokenFails) {
 }
 
 TEST_F(AttachmentDownloaderImplTest, URLFetcher_BadToken) {
-  AttachmentId id1 = attachment_id();
+  AttachmentId id1 = AttachmentId::Create();
   downloader()->DownloadAttachment(id1, download_callback(id1));
   RunMessageLoop();
   // Return valid access token.
@@ -401,7 +393,7 @@ TEST_F(AttachmentDownloaderImplTest, URLFetcher_BadToken) {
 }
 
 TEST_F(AttachmentDownloaderImplTest, URLFetcher_ServiceUnavailable) {
-  AttachmentId id1 = attachment_id();
+  AttachmentId id1 = AttachmentId::Create();
   downloader()->DownloadAttachment(id1, download_callback(id1));
   RunMessageLoop();
   // Return valid access token.
@@ -421,7 +413,7 @@ TEST_F(AttachmentDownloaderImplTest, URLFetcher_ServiceUnavailable) {
 // Verify that if no hash is present on the response the downloader accepts the
 // received attachment.
 TEST_F(AttachmentDownloaderImplTest, NoHash) {
-  AttachmentId id1 = attachment_id();
+  AttachmentId id1 = AttachmentId::Create();
   downloader()->DownloadAttachment(id1, download_callback(id1));
   RunMessageLoop();
   token_service()->RespondToAccessTokenRequest(
@@ -434,7 +426,7 @@ TEST_F(AttachmentDownloaderImplTest, NoHash) {
 // Verify that if an invalid hash is present on the response the downloader
 // treats it as a transient error.
 TEST_F(AttachmentDownloaderImplTest, InvalidHash) {
-  AttachmentId id1 = attachment_id();
+  AttachmentId id1 = AttachmentId::Create();
   downloader()->DownloadAttachment(id1, download_callback(id1));
   RunMessageLoop();
   token_service()->RespondToAccessTokenRequest(
@@ -444,21 +436,6 @@ TEST_F(AttachmentDownloaderImplTest, InvalidHash) {
   VerifyDownloadResult(id1, AttachmentDownloader::DOWNLOAD_TRANSIENT_ERROR);
 }
 
-// Verify that when the hash from the attachment id does not match the one on
-// the response the result is an unspecified error.
-TEST_F(AttachmentDownloaderImplTest, IdHashDoesNotMatch) {
-  // id1 has the wrong crc32c.
-  AttachmentId id1 = AttachmentId::Create(attachment_id().GetSize(), 12345);
-  downloader()->DownloadAttachment(id1, download_callback(id1));
-  RunMessageLoop();
-  token_service()->RespondToAccessTokenRequest(
-      GoogleServiceAuthError::AuthErrorNone());
-  RunMessageLoop();
-  CompleteDownload(net::HTTP_OK, HASH_HEADER_VALID);
-  VerifyDownloadResult(id1, AttachmentDownloader::DOWNLOAD_UNSPECIFIED_ERROR);
-}
-
-
 // Verify that extract fails when there is no headers object.
 TEST_F(AttachmentDownloaderImplTest, ExtractCrc32c_NoHeaders) {
   uint32_t extracted;
diff --git a/sync/internal_api/attachments/attachment_service_impl_unittest.cc b/sync/internal_api/attachments/attachment_service_impl_unittest.cc
index c90bcd9..e72bb8f 100644
--- a/sync/internal_api/attachments/attachment_service_impl_unittest.cc
+++ b/sync/internal_api/attachments/attachment_service_impl_unittest.cc
@@ -68,7 +68,9 @@ class MockAttachmentStore : public AttachmentStore,
     for (AttachmentIdList::const_iterator iter = ids.begin(); iter != ids.end();
          ++iter) {
       if (local_attachments.find(*iter) != local_attachments.end()) {
-        Attachment attachment = Attachment::CreateFromParts(*iter, data);
+        uint32_t crc32c = ComputeCrc32c(data);
+        Attachment attachment =
+            Attachment::CreateFromParts(*iter, data, crc32c);
         attachments->insert(std::make_pair(*iter, attachment));
       } else {
         unavailable_attachments->push_back(*iter);
@@ -125,7 +127,9 @@ class MockAttachmentDownloader
     scoped_ptr<Attachment> attachment;
     if (result == DOWNLOAD_SUCCESS) {
       scoped_refptr<base::RefCountedString> data = new base::RefCountedString();
-      attachment.reset(new Attachment(Attachment::CreateFromParts(id, data)));
+      uint32_t crc32c = ComputeCrc32c(data);
+      attachment.reset(
+          new Attachment(Attachment::CreateFromParts(id, data, crc32c)));
     }
     base::MessageLoop::current()->PostTask(
         FROM_HERE,
@@ -305,7 +309,7 @@ TEST_F(AttachmentServiceImplTest, GetOrDownload_EmptyAttachmentList) {
 
 TEST_F(AttachmentServiceImplTest, GetOrDownload_Local) {
   AttachmentIdList attachment_ids;
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
+  attachment_ids.push_back(AttachmentId::Create());
   attachment_service()->GetOrDownloadAttachments(attachment_ids,
                                                  download_callback());
   AttachmentIdSet local_attachments;
@@ -322,10 +326,10 @@ TEST_F(AttachmentServiceImplTest, GetOrDownload_Local) {
 TEST_F(AttachmentServiceImplTest, GetOrDownload_LocalRemoteUnavailable) {
   // Create attachment list with 4 ids.
   AttachmentIdList attachment_ids;
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
+  attachment_ids.push_back(AttachmentId::Create());
+  attachment_ids.push_back(AttachmentId::Create());
+  attachment_ids.push_back(AttachmentId::Create());
+  attachment_ids.push_back(AttachmentId::Create());
   // Call attachment service.
   attachment_service()->GetOrDownloadAttachments(attachment_ids,
                                                  download_callback());
@@ -391,7 +395,7 @@ TEST_F(AttachmentServiceImplTest, GetOrDownload_NoDownloader) {
       this);
 
   AttachmentIdList attachment_ids;
-  attachment_ids.push_back(AttachmentId::Create(0, 0));
+  attachment_ids.push_back(AttachmentId::Create());
   attachment_service()->GetOrDownloadAttachments(attachment_ids,
                                                  download_callback());
   EXPECT_FALSE(store()->read_ids.empty());
@@ -408,7 +412,7 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_Success) {
   AttachmentIdSet attachment_ids;
   const unsigned num_attachments = 3;
   for (unsigned i = 0; i < num_attachments; ++i) {
-    attachment_ids.insert(AttachmentId::Create(0, 0));
+    attachment_ids.insert(AttachmentId::Create());
   }
   attachment_service()->UploadAttachments(attachment_ids);
 
@@ -442,7 +446,7 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_Success_NoDelegate) {
                               NULL);  // No delegate.
 
   AttachmentIdSet attachment_ids;
-  attachment_ids.insert(AttachmentId::Create(0, 0));
+  attachment_ids.insert(AttachmentId::Create());
   attachment_service()->UploadAttachments(attachment_ids);
   RunLoopAndFireTimer();
   ASSERT_EQ(1U, store()->read_ids.size());
@@ -459,8 +463,8 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_Success_NoDelegate) {
 
 TEST_F(AttachmentServiceImplTest, UploadAttachments_SomeMissingFromStore) {
   AttachmentIdSet attachment_ids;
-  attachment_ids.insert(AttachmentId::Create(0, 0));
-  attachment_ids.insert(AttachmentId::Create(0, 0));
+  attachment_ids.insert(AttachmentId::Create());
+  attachment_ids.insert(AttachmentId::Create());
   attachment_service()->UploadAttachments(attachment_ids);
   RunLoopAndFireTimer();
   ASSERT_GE(store()->read_ids.size(), 1U);
@@ -486,7 +490,7 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_AllMissingFromStore) {
   AttachmentIdSet attachment_ids;
   const unsigned num_attachments = 2;
   for (unsigned i = 0; i < num_attachments; ++i) {
-    attachment_ids.insert(AttachmentId::Create(0, 0));
+    attachment_ids.insert(AttachmentId::Create());
   }
   attachment_service()->UploadAttachments(attachment_ids);
 
@@ -510,7 +514,7 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_NoUploader) {
                               this);
 
   AttachmentIdSet attachment_ids;
-  attachment_ids.insert(AttachmentId::Create(0, 0));
+  attachment_ids.insert(AttachmentId::Create());
   attachment_service()->UploadAttachments(attachment_ids);
   RunLoop();
   EXPECT_EQ(0U, store()->read_ids.size());
@@ -522,7 +526,7 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_OneUploadFails) {
   AttachmentIdSet attachment_ids;
   const unsigned num_attachments = 3;
   for (unsigned i = 0; i < num_attachments; ++i) {
-    attachment_ids.insert(AttachmentId::Create(0, 0));
+    attachment_ids.insert(AttachmentId::Create());
   }
   attachment_service()->UploadAttachments(attachment_ids);
 
@@ -552,7 +556,7 @@ TEST_F(AttachmentServiceImplTest, UploadAttachments_OneUploadFails) {
 TEST_F(AttachmentServiceImplTest,
        UploadAttachments_ResetBackoffAfterNetworkChange) {
   AttachmentIdSet attachment_ids;
-  attachment_ids.insert(AttachmentId::Create(0, 0));
+  attachment_ids.insert(AttachmentId::Create());
   attachment_service()->UploadAttachments(attachment_ids);
 
   RunLoopAndFireTimer();
diff --git a/sync/internal_api/attachments/attachment_store_test_template.h b/sync/internal_api/attachments/attachment_store_test_template.h
index 8e40f64..290ef22 100644
--- a/sync/internal_api/attachments/attachment_store_test_template.h
+++ b/sync/internal_api/attachments/attachment_store_test_template.h
@@ -133,8 +133,9 @@ TYPED_TEST_CASE_P(AttachmentStoreTest);
 TYPED_TEST_P(AttachmentStoreTest, Write_NoOverwriteNoError) {
   // Create two attachments with the same id but different data.
   Attachment attachment1 = Attachment::Create(this->some_data1);
-  Attachment attachment2 =
-      Attachment::CreateFromParts(attachment1.GetId(), this->some_data2);
+  uint32_t crc32c = ComputeCrc32c(this->some_data2);
+  Attachment attachment2 = Attachment::CreateFromParts(
+      attachment1.GetId(), this->some_data2, crc32c);
 
   // Write the first one.
   AttachmentList some_attachments;
diff --git a/sync/internal_api/attachments/attachment_uploader_impl_unittest.cc b/sync/internal_api/attachments/attachment_uploader_impl_unittest.cc
index 527b00e..4af6cd8 100644
--- a/sync/internal_api/attachments/attachment_uploader_impl_unittest.cc
+++ b/sync/internal_api/attachments/attachment_uploader_impl_unittest.cc
@@ -409,7 +409,7 @@ net::HttpStatusCode RequestHandler::GetStatusCode() const {
 }
 
 TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_NoPath) {
-  AttachmentId id = AttachmentId::Create(0, 0);
+  AttachmentId id = AttachmentId::Create();
   std::string unique_id = id.GetProto().unique_id();
   GURL sync_service_url("https://example.com");
   EXPECT_EQ("https://example.com/attachments/" + unique_id,
@@ -418,7 +418,7 @@ TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_NoPath) {
 }
 
 TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_JustSlash) {
-  AttachmentId id = AttachmentId::Create(0, 0);
+  AttachmentId id = AttachmentId::Create();
   std::string unique_id = id.GetProto().unique_id();
   GURL sync_service_url("https://example.com/");
   EXPECT_EQ("https://example.com/attachments/" + unique_id,
@@ -427,7 +427,7 @@ TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_JustSlash) {
 }
 
 TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_Path) {
-  AttachmentId id = AttachmentId::Create(0, 0);
+  AttachmentId id = AttachmentId::Create();
   std::string unique_id = id.GetProto().unique_id();
   GURL sync_service_url("https://example.com/service");
   EXPECT_EQ("https://example.com/service/attachments/" + unique_id,
@@ -436,7 +436,7 @@ TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_Path) {
 }
 
 TEST_F(AttachmentUploaderImplTest, GetURLForAttachmentId_PathAndSlash) {
-  AttachmentId id = AttachmentId::Create(0, 0);
+  AttachmentId id = AttachmentId::Create();
   std::string unique_id = id.GetProto().unique_id();
   GURL sync_service_url("https://example.com/service/");
   EXPECT_EQ("https://example.com/service/attachments/" + unique_id,
diff --git a/sync/internal_api/attachments/fake_attachment_downloader.cc b/sync/internal_api/attachments/fake_attachment_downloader.cc
index 299c418..53abc61 100644
--- a/sync/internal_api/attachments/fake_attachment_downloader.cc
+++ b/sync/internal_api/attachments/fake_attachment_downloader.cc
@@ -25,8 +25,9 @@ void FakeAttachmentDownloader::DownloadAttachment(
   // attachment.
   scoped_refptr<base::RefCountedMemory> data(new base::RefCountedBytes());
   scoped_ptr<Attachment> attachment;
+  const uint32_t crc32c = ComputeCrc32c(data);
   attachment.reset(
-      new Attachment(Attachment::CreateFromParts(attachment_id, data)));
+      new Attachment(Attachment::CreateFromParts(attachment_id, data, crc32c)));
   base::MessageLoop::current()->PostTask(
       FROM_HERE,
       base::Bind(callback, DOWNLOAD_SUCCESS, base::Passed(&attachment)));
diff --git a/sync/internal_api/attachments/fake_attachment_downloader_unittest.cc b/sync/internal_api/attachments/fake_attachment_downloader_unittest.cc
index 762da44..1436a49 100644
--- a/sync/internal_api/attachments/fake_attachment_downloader_unittest.cc
+++ b/sync/internal_api/attachments/fake_attachment_downloader_unittest.cc
@@ -50,7 +50,7 @@ class FakeAttachmentDownloaderTest : public testing::Test {
 };
 
 TEST_F(FakeAttachmentDownloaderTest, DownloadAttachment) {
-  AttachmentId attachment_id = AttachmentId::Create(0, 0);
+  AttachmentId attachment_id = AttachmentId::Create();
   downloader()->DownloadAttachment(attachment_id, download_callback());
   RunMessageLoop();
   EXPECT_EQ(1U, download_results().size());
diff --git a/sync/internal_api/attachments/on_disk_attachment_store.cc b/sync/internal_api/attachments/on_disk_attachment_store.cc
index b054a6e..7b715e0 100644
--- a/sync/internal_api/attachments/on_disk_attachment_store.cc
+++ b/sync/internal_api/attachments/on_disk_attachment_store.cc
@@ -316,18 +316,12 @@ scoped_ptr<Attachment> OnDiskAttachmentStore::ReadSingleAttachment(
   scoped_refptr<base::RefCountedMemory> data =
       base::RefCountedString::TakeString(&data_str);
   uint32_t crc32c = ComputeCrc32c(data);
-  if (record_metadata.has_crc32c()) {
-    if (record_metadata.crc32c() != crc32c) {
-      DVLOG(1) << "Attachment crc32c does not match value read from store";
-      return attachment.Pass();
-    }
-    if (record_metadata.crc32c() != attachment_id.GetCrc32c()) {
-      DVLOG(1) << "Attachment crc32c does not match value in AttachmentId";
-      return attachment.Pass();
-    }
+  if (record_metadata.has_crc32c() && record_metadata.crc32c() != crc32c) {
+    DVLOG(1) << "Attachment crc does not match";
+    return attachment.Pass();
   }
   attachment.reset(
-      new Attachment(Attachment::CreateFromParts(attachment_id, data)));
+      new Attachment(Attachment::CreateFromParts(attachment_id, data, crc32c)));
   return attachment.Pass();
 }
 
diff --git a/sync/internal_api/attachments/on_disk_attachment_store_unittest.cc b/sync/internal_api/attachments/on_disk_attachment_store_unittest.cc
index 231ad96..e46f060 100644
--- a/sync/internal_api/attachments/on_disk_attachment_store_unittest.cc
+++ b/sync/internal_api/attachments/on_disk_attachment_store_unittest.cc
@@ -311,9 +311,8 @@ TEST_F(OnDiskAttachmentStoreSpecificTest, RecordMetadata) {
   VerifyAttachmentRecordsPresent(attachments[1].GetId(), true);
 }
 
-// Ensure that attachment store fails to load attachment if the crc in the store
-// does not match the data.
-TEST_F(OnDiskAttachmentStoreSpecificTest, MismatchedCrcInStore) {
+// Ensure that attachment store fails to load attachment with mismatched crc.
+TEST_F(OnDiskAttachmentStoreSpecificTest, MismatchedCrc) {
   // Create attachment store.
   AttachmentStore::Result create_result = AttachmentStore::UNSPECIFIED_ERROR;
   store_ = AttachmentStore::CreateOnDiskStore(
@@ -323,12 +322,10 @@ TEST_F(OnDiskAttachmentStoreSpecificTest, MismatchedCrcInStore) {
   // Write attachment with incorrect crc32c.
   AttachmentStore::Result write_result = AttachmentStore::UNSPECIFIED_ERROR;
   const uint32_t intentionally_wrong_crc32c = 0;
-
-  scoped_refptr<base::RefCountedString> some_data(new base::RefCountedString());
-  some_data->data() = "data1";
+  std::string some_data("data1");
   Attachment attachment = Attachment::CreateFromParts(
-      AttachmentId::Create(some_data->size(), intentionally_wrong_crc32c),
-      some_data);
+      AttachmentId::Create(), base::RefCountedString::TakeString(&some_data),
+      intentionally_wrong_crc32c);
   AttachmentList attachments;
   attachments.push_back(attachment);
   store_->Write(attachments,
@@ -351,44 +348,6 @@ TEST_F(OnDiskAttachmentStoreSpecificTest, MismatchedCrcInStore) {
   EXPECT_THAT(failed_attachment_ids, testing::ElementsAre(attachment.GetId()));
 }
 
-// Ensure that attachment store fails to load attachment if the crc in the id
-// does not match the data.
-TEST_F(OnDiskAttachmentStoreSpecificTest, MismatchedCrcInId) {
-  // Create attachment store.
-  AttachmentStore::Result create_result = AttachmentStore::UNSPECIFIED_ERROR;
-  store_ = AttachmentStore::CreateOnDiskStore(
-      temp_dir_.path(), base::ThreadTaskRunnerHandle::Get(),
-      base::Bind(&AttachmentStoreCreated, &create_result));
-
-  AttachmentStore::Result write_result = AttachmentStore::UNSPECIFIED_ERROR;
-  scoped_refptr<base::RefCountedString> some_data(new base::RefCountedString());
-  some_data->data() = "data1";
-  Attachment attachment = Attachment::Create(some_data);
-  AttachmentList attachments;
-  attachments.push_back(attachment);
-  store_->Write(attachments,
-                base::Bind(&OnDiskAttachmentStoreSpecificTest::CopyResult,
-                           base::Unretained(this), &write_result));
-
-  // Read, but with the wrong crc32c in the id.
-  AttachmentStore::Result read_result = AttachmentStore::SUCCESS;
-
-  AttachmentId id_with_bad_crc32c =
-      AttachmentId::Create(attachment.GetId().GetSize(), 12345);
-  AttachmentIdList attachment_ids;
-  attachment_ids.push_back(id_with_bad_crc32c);
-  AttachmentIdList failed_attachment_ids;
-  store_->Read(
-      attachment_ids,
-      base::Bind(&OnDiskAttachmentStoreSpecificTest::CopyResultAttachments,
-                 base::Unretained(this), &read_result, &failed_attachment_ids));
-  RunLoop();
-  EXPECT_EQ(AttachmentStore::SUCCESS, create_result);
-  EXPECT_EQ(AttachmentStore::SUCCESS, write_result);
-  EXPECT_EQ(AttachmentStore::UNSPECIFIED_ERROR, read_result);
-  EXPECT_THAT(failed_attachment_ids, testing::ElementsAre(id_with_bad_crc32c));
-}
-
 // Ensure that after store initialization failure ReadWrite/Drop operations fail
 // with correct error.
 TEST_F(OnDiskAttachmentStoreSpecificTest, OpsAfterInitializationFailed) {
@@ -406,10 +365,7 @@ TEST_F(OnDiskAttachmentStoreSpecificTest, OpsAfterInitializationFailed) {
   // STORE_INITIALIZATION_FAILED.
   AttachmentStore::Result read_result = AttachmentStore::SUCCESS;
   AttachmentIdList attachment_ids;
-  std::string some_data("data1");
-  Attachment attachment =
-      Attachment::Create(base::RefCountedString::TakeString(&some_data));
-  attachment_ids.push_back(attachment.GetId());
+  attachment_ids.push_back(AttachmentId::Create());
   AttachmentIdList failed_attachment_ids;
   store_->Read(
       attachment_ids,
@@ -426,8 +382,11 @@ TEST_F(OnDiskAttachmentStoreSpecificTest, OpsAfterInitializationFailed) {
   // Writing to uninitialized store should result in
   // STORE_INITIALIZATION_FAILED.
   AttachmentStore::Result write_result = AttachmentStore::SUCCESS;
+  std::string some_data;
   AttachmentList attachments;
-  attachments.push_back(attachment);
+  some_data = "data1";
+  attachments.push_back(
+      Attachment::Create(base::RefCountedString::TakeString(&some_data)));
   store_->Write(attachments,
                 base::Bind(&OnDiskAttachmentStoreSpecificTest::CopyResult,
                            base::Unretained(this), &write_result));
diff --git a/sync/internal_api/public/attachments/attachment_downloader_impl.h b/sync/internal_api/public/attachments/attachment_downloader_impl.h
index 83bb77e..4e68f27 100644
--- a/sync/internal_api/public/attachments/attachment_downloader_impl.h
+++ b/sync/internal_api/public/attachments/attachment_downloader_impl.h
@@ -88,7 +88,8 @@ class AttachmentDownloaderImpl : public AttachmentDownloader,
   void ReportResult(
       const DownloadState& download_state,
       const DownloadResult& result,
-      const scoped_refptr<base::RefCountedString>& attachment_data);
+      const scoped_refptr<base::RefCountedString>& attachment_data,
+      uint32_t attachment_crc32c);
 
   // Extract the crc32c from an X-Goog-Hash header in |headers|.
   //
diff --git a/sync/internal_api/public/base/attachment_id_proto.cc b/sync/internal_api/public/base/attachment_id_proto.cc
index 6692ab7..52728cd 100644
--- a/sync/internal_api/public/base/attachment_id_proto.cc
+++ b/sync/internal_api/public/base/attachment_id_proto.cc
@@ -10,16 +10,13 @@
 
 namespace syncer {
 
-sync_pb::AttachmentIdProto CreateAttachmentIdProto(size_t size,
-                                                   uint32_t crc32c) {
+sync_pb::AttachmentIdProto CreateAttachmentIdProto() {
   sync_pb::AttachmentIdProto proto;
   std::string guid = base::StringToLowerASCII(base::GenerateGUID());
   DCHECK(!guid.empty());
   // Requirements are that this id must be a unique RFC4122 UUID, formatted in
   // lower case.
   proto.set_unique_id(guid);
-  proto.set_size_bytes(size);
-  proto.set_crc32c(crc32c);
   return proto;
 }
 
diff --git a/sync/internal_api/public/base/attachment_id_proto.h b/sync/internal_api/public/base/attachment_id_proto.h
index 9af3a986..a47f46e 100644
--- a/sync/internal_api/public/base/attachment_id_proto.h
+++ b/sync/internal_api/public/base/attachment_id_proto.h
@@ -5,7 +5,6 @@
 #ifndef SYNC_INTERNAL_API_PUBLIC_BASE_ATTACHMENT_ID_PROTO_H_
 #define SYNC_INTERNAL_API_PUBLIC_BASE_ATTACHMENT_ID_PROTO_H_
 
-#include "base/basictypes.h"
 #include "sync/base/sync_export.h"
 #include "sync/protocol/sync.pb.h"
 
@@ -14,13 +13,7 @@ namespace syncer {
 // Helper functions that are logically part of sync_pb::AttachmentIdProto.
 
 // Creates a unique AttachmentIdProto.
-//
-// |size| is the size in bytes of the attachment identified by this proto.
-//
-// |crc32c| is the crc32c of the attachment identified by this proto.
-SYNC_EXPORT_PRIVATE sync_pb::AttachmentIdProto CreateAttachmentIdProto(
-    size_t size,
-    uint32_t crc32c);
+SYNC_EXPORT_PRIVATE sync_pb::AttachmentIdProto CreateAttachmentIdProto();
 
 // Creates an AttachmentMetadata object from a repeated field of
 // AttachmentIdProto objects.
diff --git a/sync/internal_api/public/base/attachment_id_proto_unittest.cc b/sync/internal_api/public/base/attachment_id_proto_unittest.cc
index 2f9d3f0..5321e2b 100644
--- a/sync/internal_api/public/base/attachment_id_proto_unittest.cc
+++ b/sync/internal_api/public/base/attachment_id_proto_unittest.cc
@@ -15,7 +15,7 @@ typedef testing::Test AttachmentIdProtoTest;
 // Verify that that we generate a proto with a properly formatted unique_id
 // field.
 TEST(AttachmentIdProtoTest, UniqueIdFormat) {
-  sync_pb::AttachmentIdProto id_proto = CreateAttachmentIdProto(0, 0);
+  sync_pb::AttachmentIdProto id_proto = CreateAttachmentIdProto();
   ASSERT_TRUE(id_proto.has_unique_id());
   // gtest's regular expression support is pretty poor so we cannot test as
   // closely as we would like.
@@ -35,9 +35,9 @@ TEST(AttachmentIdProtoTest, CreateAttachmentMetadata_Empty) {
 
 TEST(AttachmentIdProtoTest, CreateAttachmentMetadata_NonEmpty) {
   google::protobuf::RepeatedPtrField<sync_pb::AttachmentIdProto> ids;
-  *ids.Add() = CreateAttachmentIdProto(0, 0);
-  *ids.Add() = CreateAttachmentIdProto(0, 0);
-  *ids.Add() = CreateAttachmentIdProto(0, 0);
+  *ids.Add() = CreateAttachmentIdProto();
+  *ids.Add() = CreateAttachmentIdProto();
+  *ids.Add() = CreateAttachmentIdProto();
   sync_pb::AttachmentMetadata metadata = CreateAttachmentMetadata(ids);
   ASSERT_EQ(3, metadata.record_size());
   for (int i = 0; i < metadata.record_size(); ++i) {
diff --git a/sync/internal_api/sync_manager_impl_unittest.cc b/sync/internal_api/sync_manager_impl_unittest.cc
index 75fbe10..5e69ec5 100644
--- a/sync/internal_api/sync_manager_impl_unittest.cc
+++ b/sync/internal_api/sync_manager_impl_unittest.cc
@@ -676,7 +676,7 @@ TEST_F(SyncApiTest, GetTotalNodeCountMultipleChildren) {
 TEST_F(SyncApiTest, AttachmentLinking) {
   // Add an entry with an attachment.
   std::string tag1("some tag");
-  syncer::AttachmentId attachment_id(syncer::AttachmentId::Create(0, 0));
+  syncer::AttachmentId attachment_id(syncer::AttachmentId::Create());
   sync_pb::AttachmentMetadata attachment_metadata;
   sync_pb::AttachmentMetadataRecord* record = attachment_metadata.add_record();
   *record->mutable_id() = attachment_id.GetProto();
@@ -3112,7 +3112,7 @@ TEST_F(SyncManagerChangeProcessingTest, AttachmentMetadataOnlyChanges) {
         FROM_HERE, syncable::SYNCER, share()->directory.get());
     syncable::MutableEntry article(&trans, syncable::GET_BY_HANDLE, article_id);
     sync_pb::AttachmentMetadata metadata;
-    *metadata.add_record()->mutable_id() = CreateAttachmentIdProto(0, 0);
+    *metadata.add_record()->mutable_id() = CreateAttachmentIdProto();
     article.PutAttachmentMetadata(metadata);
   }
   ASSERT_EQ(1UL, GetChangeListSize());
@@ -3126,7 +3126,7 @@ TEST_F(SyncManagerChangeProcessingTest, AttachmentMetadataOnlyChanges) {
         FROM_HERE, syncable::SYNCER, share()->directory.get());
     syncable::MutableEntry article(&trans, syncable::GET_BY_HANDLE, article_id);
     sync_pb::AttachmentMetadata metadata = article.GetAttachmentMetadata();
-    *metadata.add_record()->mutable_id() = CreateAttachmentIdProto(0, 0);
+    *metadata.add_record()->mutable_id() = CreateAttachmentIdProto();
     article.PutAttachmentMetadata(metadata);
   }
   ASSERT_EQ(1UL, GetChangeListSize());
diff --git a/sync/protocol/attachments.proto b/sync/protocol/attachments.proto
index 986e29f..e08e2b0 100644
--- a/sync/protocol/attachments.proto
+++ b/sync/protocol/attachments.proto
@@ -19,10 +19,6 @@ message AttachmentIdProto {
   // Uniquely identifies the attachment. Two attachments with the same unique_id
   // are considered equivalent.
   optional string unique_id = 1;
-  // Size of the attachment data in bytes.
-  optional uint64 size_bytes = 2;
-  // Crc32c of the attachment data.
-  optional uint32 crc32c = 3;
 }
 
 // Metadata for a single attachment.
diff --git a/sync/syncable/directory_unittest.cc b/sync/syncable/directory_unittest.cc
index 5f8cbed..64f3b57 100644
--- a/sync/syncable/directory_unittest.cc
+++ b/sync/syncable/directory_unittest.cc
@@ -1639,7 +1639,7 @@ TEST_F(SyncableDirectoryTest, MutableEntry_PutAttachmentMetadata) {
   sync_pb::AttachmentMetadata attachment_metadata;
   sync_pb::AttachmentMetadataRecord* record = attachment_metadata.add_record();
   sync_pb::AttachmentIdProto attachment_id_proto =
-      syncer::CreateAttachmentIdProto(0, 0);
+      syncer::CreateAttachmentIdProto();
   *record->mutable_id() = attachment_id_proto;
   ASSERT_FALSE(dir()->IsAttachmentLinked(attachment_id_proto));
   {
@@ -1683,8 +1683,8 @@ TEST_F(SyncableDirectoryTest, MutableEntry_UpdateAttachmentId) {
   sync_pb::AttachmentMetadata attachment_metadata;
   sync_pb::AttachmentMetadataRecord* r1 = attachment_metadata.add_record();
   sync_pb::AttachmentMetadataRecord* r2 = attachment_metadata.add_record();
-  *r1->mutable_id() = syncer::CreateAttachmentIdProto(0, 0);
-  *r2->mutable_id() = syncer::CreateAttachmentIdProto(0, 0);
+  *r1->mutable_id() = syncer::CreateAttachmentIdProto();
+  *r2->mutable_id() = syncer::CreateAttachmentIdProto();
   sync_pb::AttachmentIdProto attachment_id_proto = r1->id();
 
   WriteTransaction trans(FROM_HERE, UNITTEST, dir().get());
@@ -1713,7 +1713,7 @@ TEST_F(SyncableDirectoryTest, Directory_DeleteDoesNotUnlinkAttachments) {
   sync_pb::AttachmentMetadata attachment_metadata;
   sync_pb::AttachmentMetadataRecord* record = attachment_metadata.add_record();
   sync_pb::AttachmentIdProto attachment_id_proto =
-      syncer::CreateAttachmentIdProto(0, 0);
+      syncer::CreateAttachmentIdProto();
   *record->mutable_id() = attachment_id_proto;
   ASSERT_FALSE(dir()->IsAttachmentLinked(attachment_id_proto));
   const Id id = TestIdFactory::FromNumber(-1);
@@ -1742,7 +1742,7 @@ TEST_F(SyncableDirectoryTest, Directory_LastReferenceUnlinksAttachments) {
   sync_pb::AttachmentMetadata attachment_metadata;
   sync_pb::AttachmentMetadataRecord* record = attachment_metadata.add_record();
   sync_pb::AttachmentIdProto attachment_id_proto =
-      syncer::CreateAttachmentIdProto(0, 0);
+      syncer::CreateAttachmentIdProto();
   *record->mutable_id() = attachment_id_proto;
 
   // Create two entries, each referencing the attachment.
@@ -1771,7 +1771,7 @@ TEST_F(SyncableDirectoryTest, Directory_LastReferenceUnlinksAttachments) {
 
 TEST_F(SyncableDirectoryTest, Directory_GetAttachmentIdsToUpload) {
   // Create one attachment, referenced by two entries.
-  AttachmentId attachment_id = AttachmentId::Create(0, 0);
+  AttachmentId attachment_id = AttachmentId::Create();
   sync_pb::AttachmentIdProto attachment_id_proto = attachment_id.GetProto();
   sync_pb::AttachmentMetadata attachment_metadata;
   sync_pb::AttachmentMetadataRecord* record = attachment_metadata.add_record();