Revert "Mojo: NodeChannel should require a minimum size when using multiple versions"

This reverts commit 8ad25003.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 828478 as the
culprit for flakes in the build cycles as shown on:
https://analysis.chromium.org/p/chromium/flake-portal/analysis/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyQwsSDEZsYWtlQ3VscHJpdCIxY2hyb21pdW0vOGFkMjUwMDNkZTgwODIxMjhjM2IzNDU2NWVhMjg4ZGM3OGZhODhkYgw

Sample Failed Build: https://ci.chromium.org/b/8863329295603494640

Sample Failed Step: mojo_unittests on (none) GPU on Mac on Mac-10.14.6

Sample Flaky Test: NodeChannelTest.MessagesCannotBeSmallerThanOldestVersion

Original change's description:
> Mojo: NodeChannel should require a minimum size when using multiple versions
> 
> When we added support for versioned message we accidentally introduced a
> behavior where messages can be shorter than expected. This is what the
> behavior should be to allow older messages to be received. However,
> we know the minimum size is the oldest message version. We should
> never be allowed to go smaller than that.
> 
> BUG=chromium:1149805
> 
> Change-Id: I3a24dd62b6fafd742cd7ac155f863d33bb5c6de8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545207
> Reviewed-by: Ken Rockot <rockot@google.com>
> Commit-Queue: Brian Geffon <bgeffon@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#828478}


No-Presubmit: true
No-Tree-Checks: true
No-Try: true
BUG=chromium:1149805

Change-Id: I0bb4a4605a1f705c4388769fae4559e0835d1980
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2546460
Cr-Commit-Position: refs/heads/master@{#828581}

mojo/core/node_channel.cc

@@ -190,16 +190,13 @@ Channel::MessagePtr CreateMessage(MessageType type,
   return msg_ptr;
 }
 
-// This method takes a second template argument which is another datatype which
-// represents the smallest size this payload can be to be considered valid this
-// MUST be used when there is more than one version of a message to specify the
-// oldest version of the message.
-template <typename DataType, typename MinSizedDataType>
-bool GetMessagePayloadMinimumSized(const void* bytes,
+template <typename DataType>
+bool GetMessagePayload(const void* bytes,
                        size_t num_bytes,
                        DataType* out_data) {
   static_assert(sizeof(DataType) > 0, "DataType must have non-zero size.");
-  if (num_bytes < sizeof(Header) + sizeof(MinSizedDataType))
+  // We should have at least 1 byte to contribute towards DataType.
+  if (num_bytes <= sizeof(Header))
     return false;
 
   // Always make sure that the full object is zeored and default constructed as
@@ -214,14 +211,6 @@ bool GetMessagePayloadMinimumSized(const void* bytes,
   return true;
 }
 
-template <typename DataType>
-bool GetMessagePayload(const void* bytes,
-                       size_t num_bytes,
-                       DataType* out_data) {
-  return GetMessagePayloadMinimumSized<DataType, DataType>(bytes, num_bytes,
-                                                           out_data);
-}
-
 }  // namespace
 
 // static

mojo/core/node_channel_unittest.cc

@@ -5,7 +5,6 @@
 #include "mojo/core/node_channel.h"
 
 #include "base/callback_helpers.h"
-#include "base/logging.h"
 #include "base/memory/scoped_refptr.h"
 #include "base/message_loop/message_pump_type.h"
 #include "base/test/task_environment.h"
@@ -22,7 +21,6 @@ namespace {
 
 using NodeChannelTest = testing::Test;
 using ports::NodeName;
-using testing::_;
 
 scoped_refptr<NodeChannel> CreateNodeChannel(NodeChannel::Delegate* delegate,
                                              PlatformChannelEndpoint endpoint) {
@@ -69,48 +67,6 @@ TEST_F(NodeChannelTest, DestructionIsSafe) {
   error_loop.Run();
 }
 
-TEST_F(NodeChannelTest, MessagesCannotBeSmallerThanOldestVersion) {
-  base::test::TaskEnvironment task_environment;
-
-  PlatformChannel channel;
-  MockNodeChannelDelegate local_delegate;
-  auto local_channel =
-      CreateNodeChannel(&local_delegate, channel.TakeLocalEndpoint());
-  local_channel->Start();
-  MockNodeChannelDelegate remote_delegate;
-  auto remote_channel =
-      CreateNodeChannel(&remote_delegate, channel.TakeRemoteEndpoint());
-  remote_channel->Start();
-
-  base::RunLoop loop;
-
-  // It's a bad message and shouldn't be passed to the delegate.
-  EXPECT_CALL(local_delegate, OnRequestPortMerge(_, _, _)).Times(0);
-
-  // This good message should go through after.
-  const NodeName kRemoteNodeName{123, 456};
-  const NodeName kToken{987, 654};
-  EXPECT_CALL(local_delegate,
-              OnAcceptInvitee(ports::kInvalidNodeName, kRemoteNodeName, kToken))
-      .WillRepeatedly([&] {
-    loop.Quit(); });
-
-  // 1 byte is not enough to contain the oldest version of the request port
-  // merge payload, it should be discarded.
-  int payload_size = 1;
-  int capacity = /*sizeof(header)=*/8 + payload_size;
-  auto message =
-      std::make_unique<Channel::Message>(capacity, capacity, /*num_handles=*/0);
-
-  // Set the type of this message as REQUEST_PORT_MERGE (6)
-  *reinterpret_cast<uint32_t*>(message->mutable_payload()) = 6;
-
-  // This short message should be ignored.
-  remote_channel->SendChannelMessage(std::move(message));
-  remote_channel->AcceptInvitee(kRemoteNodeName, kToken);
-  loop.Run();
-}
-
 }  // namespace
 }  // namespace core
 }  // namespace mojo