Add support for taking partial screenshot using touch

ash/wm/partial_screenshot_view.cc

Index: ash/wm/partial_screenshot_view.cc
diff --git a/ash/wm/partial_screenshot_view.cc b/ash/wm/partial_screenshot_view.cc
index 03116e7cf941e30e3b8ef3ecbbbec902a3895c12..f09f381a88d4fa04115c73ff4ef5b4877c716001 100644
--- a/ash/wm/partial_screenshot_view.cc
+++ b/ash/wm/partial_screenshot_view.cc
@@ -94,7 +94,8 @@ void PartialScreenshotView::StartPartialScreenshot(
 PartialScreenshotView::PartialScreenshotView(
     PartialScreenshotView::OverlayDelegate* overlay_delegate,
     ScreenshotDelegate* screenshot_delegate)
-    : is_dragging_(false),
+    : current_touch_id_(-1),
+      is_dragging_(false),
       overlay_delegate_(overlay_delegate),
       screenshot_delegate_(screenshot_delegate) {
 }
@@ -198,4 +199,27 @@ void PartialScreenshotView::OnMouseReleased(const ui::MouseEvent& event) {
   }
 }
 
+void PartialScreenshotView::OnTouchEvent(ui::TouchEvent* event) {

[sadrul, 2013/03/25 21:11:04]

You should override OnGestureEvent, and use scroll-gesture events
(ET_GESTURE_SCROLL_BEGIN, SCROLL_UPDATE, and SCROLL_END/ET_SCROLL_FLING_START)
for this.

[Yufeng Shen (Slow to review), 2013/03/25 22:03:34]

Done.

+  gfx::Point position = event->location();
+
+  if (current_touch_id_ != -1 && current_touch_id_ != event->touch_id())

[Jun Mukai, 2013/03/25 21:03:48]

So, this will ignore the second finger touch right?
That would be fine, but not so sure the expected behavior. When the user touch
the screen by two fingers, the user might expect to select the region by those
two fingers?
I'm okay to go ahead with this code, but please discuss about this later in the
crbug.

[Yufeng Shen (Slow to review), 2013/03/25 22:03:34]

I will put a note in the crbug.

+    return;
+
+  if (event->type() == ui::ET_TOUCH_PRESSED) {
+    current_touch_id_ = event->touch_id();
+    ui::MouseEvent mouse_event(ui::ET_MOUSE_PRESSED, position, position, 0);
+    OnMousePressed(mouse_event);
+  } else if (event->type() == ui::ET_TOUCH_MOVED) {
+    ui::MouseEvent mouse_event(ui::ET_MOUSE_DRAGGED, position, position, 0);
+    OnMouseDragged(mouse_event);
+  } else if (event->type() == ui::ET_TOUCH_RELEASED ||
+             event->type() == ui::ET_TOUCH_CANCELLED) {
+    current_touch_id_ = -1;
+    ui::MouseEvent mouse_event(ui::ET_MOUSE_RELEASED, position, position, 0);
+    OnMouseReleased(mouse_event);
+  }

[Jun Mukai, 2013/03/25 21:03:48]

This is okay, but creating dummy mouse event doesn't look excellent. What about:
- extract the logic into other methods, for example
OnSelectionStarted()/OnSelectionChanged()/OnSelectionFinished(), which accepts
location only
- and call them both from Mouse event handlers and here

[sadrul, 2013/03/25 21:11:04]

+1. This is usually how it's done in other parts of the code.

[Yufeng Shen (Slow to review), 2013/03/25 22:03:34]

Done.

+
+  event->SetHandled();
+}
+
 }  // namespace ash