Fixed BUILD.gn filename typo: file_data_pipe_producer.g

file_data_pipe_producer.g should have been file_data_pipe_producer.h

TBR=rockot@chromium.org

Bug: None
Change-Id: Ia25c80f2c62198fe6114d1a170542f710242e016
Reviewed-on: https://chromium-review.googlesource.com/836453
Commit-Queue: Chris Mumford <cmumford@chromium.org>
Reviewed-by: Chris Mumford <cmumford@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527100}

mojo/public/cpp/system/BUILD.gn

@@ -28,7 +28,7 @@ component("system") {
     "core.h",
     "data_pipe.h",
     "file_data_pipe_producer.cc",
-    "file_data_pipe_producer.g",
+    "file_data_pipe_producer.h",
     "functions.h",
     "handle.h",
     "handle_signal_tracker.cc",