Add Mojo IPC based input-device service.

ui/events/devices/input_device.cc

Index: ui/events/devices/input_device.cc
diff --git a/ui/events/devices/input_device.cc b/ui/events/devices/input_device.cc
index 4734edd0280986dc11f231b3a65394e6db004d4b..aeac8a5eaa01185f82c242d81dc994162d2d16e2 100644
--- a/ui/events/devices/input_device.cc
+++ b/ui/events/devices/input_device.cc
@@ -6,8 +6,26 @@
 
 #include <string>
 
+#include "base/strings/stringprintf.h"
+
 namespace ui {
 
+namespace {
+
+std::string InputDeviceTypeString(InputDeviceType type) {
+#define ECASE(value) \
+  case value:        \
+    return #value
+  switch (type) {
+    ECASE(INPUT_DEVICE_INTERNAL);
+    ECASE(INPUT_DEVICE_EXTERNAL);
+    ECASE(INPUT_DEVICE_UNKNOWN);
+  }
+#undef ECASE
+}
+
+}  // namespace
+
 // static
 const int InputDevice::kInvalidId = 0;
 
@@ -37,4 +55,9 @@ InputDevice::InputDevice(const InputDevice& other) = default;
 InputDevice::~InputDevice() {
 }
 
+std::string InputDevice::ToString() const {
+  return base::StringPrintf("InputDevice[id=%d, name=\"%s\", type=%s]", id,
+                            name.c_str(), InputDeviceTypeString(type).c_str());
+}
+
 }  // namespace ui