Wire up Android back button in SkyShell

The back button now triggers an event of type |back|.

R=eseidel@chromium.org, jackson@chromium.org

Review URL: https://codereview.chromium.org/1176373004.

engine/public/platform/WebInputEvent.h

@@ -123,6 +123,8 @@ public:
         GestureTypeLast = GesturePinchUpdate,
 
         WheelEvent,
+
+        Back,
     };
 
     enum Modifiers {
@@ -187,6 +189,10 @@ public:
         return type == WheelEvent;
     }
 
+    static WebInputEvent* create() {
+        return new WebInputEvent(sizeof(WebInputEvent));
+    }
+
 protected:
     explicit WebInputEvent(unsigned sizeParam)
     {

engine/public/sky/sky_view.cc

@@ -91,6 +91,8 @@ void SkyView::HandleInputEvent(const WebInputEvent& inputEvent) {
   } else if (WebInputEvent::isWheelEventType(inputEvent.type)) {
       const WebWheelEvent& event = static_cast<const WebWheelEvent&>(inputEvent);
       data_->view_->handleInputEvent(WheelEvent::create(event));
+  } else if (inputEvent.type == WebInputEvent::Back) {
+      data_->view_->handleInputEvent(Event::create("back"));
   }
 
 }

examples/raw/hello_world.dart

@@ -30,6 +30,11 @@ bool handleEvent(Event event) {
     return true;
   }
 
+  if (event.type == "back") {
+    print("Pressed back button.");
+    return true;
+  }
+
   return false;
 }
 

services/viewport/input_event.mojom

@@ -19,6 +19,7 @@ enum EventType {
   GESTURE_SHOW_PRESS,
   GESTURE_TAP,
   GESTURE_TAP_DOWN,
+  BACK,
 };
 
 enum PointerKind {

shell/android/org/domokit/sky/shell/PlatformViewAndroid.java

@@ -176,6 +176,12 @@ public class PlatformViewAndroid extends SurfaceView
         mViewportObserver.onInputEvent(event);
     }
 
+    public void onBackPressed() {
+        InputEvent event = new InputEvent();
+        event.type = EventType.BACK;
+        mViewportObserver.onInputEvent(event);
+    }
+
     public void loadUrl(String url) {
         mViewportObserver.loadUrl(url);
     }

shell/android/org/domokit/sky/shell/SkyActivity.java

@@ -48,6 +48,17 @@ public class SkyActivity extends Activity {
         super.onDestroy();
     }
 
+    @Override
+    public void onBackPressed() {
+        if (mView != null) {
+            mView.onBackPressed();
+            // TODO(abarth): We should have some way to trigger the default
+            // back behavior.
+            return;
+        }
+        super.onBackPressed();
+    }
+
     public void loadUrl(String url) {
         mView.loadUrl(url);
     }

shell/ui/input_event_converter.cc

@@ -104,6 +104,12 @@ scoped_ptr<blink::WebInputEvent> BuildWebGestureEvent(
   return web_event.Pass();
 }
 
+scoped_ptr<blink::WebInputEvent> BuildWebBackEvent(const InputEventPtr& event) {
+  scoped_ptr<blink::WebInputEvent> web_event(blink::WebInputEvent::create());
+  web_event->type = blink::WebInputEvent::Back;
+  return web_event.Pass();
+}
+
 }  // namespace
 
 scoped_ptr<blink::WebInputEvent> ConvertEvent(const InputEventPtr& event,
@@ -124,6 +130,8 @@ scoped_ptr<blink::WebInputEvent> ConvertEvent(const InputEventPtr& event,
     case EVENT_TYPE_GESTURE_TAP:
     case EVENT_TYPE_GESTURE_TAP_DOWN:
       return BuildWebGestureEvent(event, device_pixel_ratio);
+    case EVENT_TYPE_BACK:
+      return BuildWebBackEvent(event);
     case EVENT_TYPE_UNKNOWN:
       NOTIMPLEMENTED() << "ConvertEvent received unexpected EVENT_TYPE_UNKNOWN";
   }