Mojo: Fix data pipe ALL_OR_NONE write capacity check.

mojo/edk/system/data_pipe_producer_dispatcher.cc

Index: mojo/edk/system/data_pipe_producer_dispatcher.cc
diff --git a/mojo/edk/system/data_pipe_producer_dispatcher.cc b/mojo/edk/system/data_pipe_producer_dispatcher.cc
index 5c7b75df76665e439a1d528136c593ce100d4578..8273c14d18fc144adf2255568922ffd1f0413565 100644
--- a/mojo/edk/system/data_pipe_producer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_producer_dispatcher.cc
@@ -137,9 +137,8 @@ MojoResult DataPipeProducerDispatcher::WriteData(const void* elements,
   if (*num_bytes == 0)
     return MOJO_RESULT_OK;  // Nothing to do.
 
-  bool all_or_none = flags & MOJO_WRITE_DATA_FLAG_ALL_OR_NONE;
-  uint32_t min_num_bytes_to_write = all_or_none ? *num_bytes : 0;
-  if (min_num_bytes_to_write > options_.capacity_num_bytes) {
+  if ((flags & MOJO_WRITE_DATA_FLAG_ALL_OR_NONE) &&
+      (*num_bytes > available_capacity_)) {
     // Don't return "should wait" since you can't wait for a specified amount of
     // data.
     return MOJO_RESULT_OUT_OF_RANGE;

[miu, 2016/09/14 22:40:23]

Should this instead be:

1. MOJO_RESULT_SHOULD_WAIT if available_capacity_ is insufficient.
and
2. MOJO_RESULT_OUT_OF_RANGE if options_.capacity_num_bytes is insufficient.

Let me know if I should change this behavior.

[jam, 2016/09/15 17:08:34]

the canonical documentation is in
https://cs.chromium.org/chromium/src/mojo/public/c/system/data_pipe.h?rcl=0&l...,
which says 

"//   |MOJO_RESULT_SHOULD_WAIT| if no data can currently be written (and the
//       consumer is still open) and |flags| does *not* have
//       |MOJO_WRITE_DATA_FLAG_ALL_OR_NONE| set."

so your current implementation is good