Crash when sending oversized legacy IPC messages

We have a clear indication that some renderer code paths are sending
oversized IPC messages (https://crbug.com/766032), but because of
thread-hopping via IPC::ChannelProxy the details remain unclear.

This adds a message size CHECK earlier in the stack, before (if) any
task is posted to the IPC thread to do the Send.

BUG=766032

Change-Id: I68e3962076a97b5774d12d971039b303fc755f4d
Reviewed-on: https://chromium-review.googlesource.com/671446
Commit-Queue: Ken Rockot <rockot@chromium.org>
Reviewed-by: Yuzhu Shen <yzshen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502641}

ipc/ipc_channel.cc

@@ -23,6 +23,9 @@ base::AtomicSequenceNumber g_last_id;
 
 namespace IPC {
 
+// static
+constexpr size_t Channel::kMaximumMessageSize;
+
 // static
 std::string Channel::GenerateUniqueRandomChannelID() {
   // Note: the string must start with the current process id, this is how

ipc/ipc_channel.h

@@ -140,7 +140,7 @@ class IPC_EXPORT Channel : public Sender {
 
   // The maximum message size in bytes. Attempting to receive a message of this
   // size or bigger results in a channel error.
-  static const size_t kMaximumMessageSize = 128 * 1024 * 1024;
+  static constexpr size_t kMaximumMessageSize = 128 * 1024 * 1024;
 
   // Amount of data to read at once from the pipe.
   static const size_t kReadBufferSize = 4 * 1024;

ipc/ipc_channel_nacl.cc

@@ -67,6 +67,9 @@ bool ReadDataOnReaderThread(int pipe, MessageContents* contents) {
 
 }  // namespace
 
+// static
+constexpr size_t Channel::kMaximumMessageSize;
+
 class ChannelNacl::ReaderThreadRunner
     : public base::DelegateSimpleThread::Delegate {
  public:

ipc/ipc_channel_proxy.cc

@@ -531,6 +531,10 @@ void ChannelProxy::SendInternal(Message* message) {
   Logging::GetInstance()->OnSendMessage(message);
 #endif
 
+  // See https://crbug.com/766032. This is to ensure that senders of oversized
+  // messages can be caught more easily in the wild.
+  CHECK_LE(message->size(), Channel::kMaximumMessageSize);
+
   context_->Send(message);
 }