Add input event struct traits to convert to mojo data types and back.

The InputEvent struct traits currently convert from
WebInputEvent<--mojo-->WebInputEvent. Eventually we will use
the struct traits to convert ui::Event<--mojo-->WebInputEvent when
we only use WebInputEvents inside the renderer.

BUG=722928

Change-Id: I8653d74a0342da28c92ba2b31d5f98effbac54d1
Reviewed-on: https://chromium-review.googlesource.com/543197
Reviewed-by: Antoine Labour <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Commit-Queue: Dave Tapuska <[email protected]>
Cr-Commit-Position: refs/heads/master@{#485057}
diff --git a/content/common/BUILD.gn b/content/common/BUILD.gn
index f4b07aa8247..0cc4552 100644
--- a/content/common/BUILD.gn
+++ b/content/common/BUILD.gn
@@ -176,6 +176,8 @@
     "input/input_event_dispatch_type.h",
     "input/input_event_stream_validator.cc",
     "input/input_event_stream_validator.h",
+    "input/input_event_struct_traits.cc",
+    "input/input_event_struct_traits.h",
     "input/input_param_traits.cc",
     "input/input_param_traits.h",
     "input/synthetic_gesture_packet.cc",