Improved FileDataPipeProducer errors part 2.

1. Returned more specific errors in OnHandleReady/TransferSomeBytes.
2. Described returned errors in header documentation.
3. Not mapping MOJO_RESULT_ALREADY_EXISTS as that will not be
   returned.

Bug: none
Change-Id: Icaa78bd347995c175cc50eb807d9a400d21e96e4
Reviewed-on: https://chromium-review.googlesource.com/809324Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Chris Mumford <cmumford@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522106}

mojo/public/cpp/system/file_data_pipe_producer.cc

@@ -32,8 +32,6 @@ MojoResult FileErrorToMojoResult(base::File::Error error) {
   switch (error) {
     case base::File::FILE_OK:
       return MOJO_RESULT_OK;
-    case base::File::FILE_ERROR_EXISTS:
-      return MOJO_RESULT_ALREADY_EXISTS;
     case base::File::FILE_ERROR_NOT_FOUND:
       return MOJO_RESULT_NOT_FOUND;
     case base::File::FILE_ERROR_SECURITY:
@@ -132,7 +130,7 @@ class FileDataPipeProducer::FileSequenceState
     if (result != MOJO_RESULT_OK) {
       // Either the consumer pipe has been closed or something terrible
       // happened. In any case, we'll never be able to write more data.
-      Finish(MOJO_RESULT_ABORTED);
+      Finish(result);
       return;
     }
 
@@ -149,7 +147,7 @@ class FileDataPipeProducer::FileSequenceState
       if (result == MOJO_RESULT_SHOULD_WAIT)
         return;
       if (result != MOJO_RESULT_OK) {
-        Finish(MOJO_RESULT_ABORTED);
+        Finish(result);
         return;
       }
 

mojo/public/cpp/system/file_data_pipe_producer.h

@@ -39,8 +39,14 @@ class MOJO_CPP_SYSTEM_EXPORT FileDataPipeProducer {
   //
   // If the write is successful |result| will be |MOJO_RESULT_OK|. Otherwise
   // (e.g. if the producer detects the consumer is closed and the pipe has no
-  // remaining capacity, or if file reads fail for any reason) |result| will be
-  // |MOJO_RESULT_ABORTED|.
+  // remaining capacity, or if file open/reads fail for any reason) |result|
+  // will be one of the following:
+  //
+  //   |MOJO_RESULT_ABORTED|
+  //   |MOJO_RESULT_NOT_FOUND|
+  //   |MOJO_RESULT_PERMISSION_DENIED|
+  //   |MOJO_RESULT_RESOURCE_EXHAUSTED|
+  //   |MOJO_RESULT_UNKNOWN|
   //
   // Note that if the FileDataPipeProducer is destroyed before |callback| can be
   // invoked, |callback| is *never* invoked, and the write will be permanently