Fix multi-touch to work in SkyShell.

sky/engine/core/frame/NewEventHandler.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/frame/NewEventHandler.h"
 
 #include "sky/engine/core/dom/Document.h"
 #include "sky/engine/core/dom/NodeRenderingTraversal.h"
 #include "sky/engine/core/editing/Editor.h"
@@ skipping 103 matching lines @@
     Node* clickTarget = NodeRenderingTraversal::commonAncestor(*releaseTarget, capturingTarget);
     if (!clickTarget)
         return true;
     // TODO(abarth): Make a proper gesture event that includes information from the event.
     return clickTarget->dispatchEvent(Event::createCancelableBubble(EventTypeNames::click));
 }
 
 void NewEventHandler::updateSelectionForPointerDown(const HitTestResult& hitTestResult, const WebPointerEvent& event)
 {
     Node* innerNode = hitTestResult.innerNode();
-    if (!innerNode->renderer())
+    if (!innerNode || !innerNode->renderer())
         return;
     if (Position::nodeIsUserSelectNone(innerNode))
         return;
     if (!innerNode->dispatchEvent(Event::createCancelableBubble(EventTypeNames::selectstart)))
         return;
     VisiblePosition position = visiblePositionForHitTestResult(hitTestResult);
     // TODO(abarth): Can we change this to setSelectionIfNeeded?
     m_frame.selection().setNonDirectionalSelectionIfNeeded(VisibleSelection(position), CharacterGranularity);
 }
 
@@ skipping 49 matching lines @@
     RefPtr<Node> target = targetForHitTestResult(hitTestResult);
     return target && !dispatchWheelEvent(*target, event);
 }
 
 bool NewEventHandler::handlePointerDownEvent(const WebPointerEvent& event)
 {
     // In principle, we shouldn't get another pointer down for the same
     // pointer ID, but for mice, we don't get a pointer cancel when you
     // drag outside the window frame on Linux. For now, send the pointer
     // cancel at this point.
-    if (event.kind == WebPointerEvent::Mouse
-        && m_stateForPointer.find(event.pointer) != m_stateForPointer.end()) {
+    bool alreadyDown = m_stateForPointer.find(event.pointer) != m_stateForPointer.end();
+    if (event.kind == WebPointerEvent::Mouse && alreadyDown) {
         WebPointerEvent fakeCancel = event;
         fakeCancel.type = WebInputEvent::PointerCancel;
         handlePointerCancelEvent(fakeCancel);
     }
 
-    ASSERT(m_stateForPointer.find(event.pointer) == m_stateForPointer.end());
+    DCHECK(!alreadyDown) << "Pointer id " << event.pointer << "already down!";
     HitTestResult hitTestResult = performHitTest(positionForEvent(event));
     RefPtr<Node> target = targetForHitTestResult(hitTestResult);
     if (!target)
         return false;
     PointerState& state = m_stateForPointer[event.pointer];
     state.target = target;
     bool eventSwallowed = !dispatchPointerEvent(state, event);
     // TODO(abarth): Set the target for the pointer to something determined when
     // dispatching the event.
     updateSelectionForPointerDown(hitTestResult, event);
@@ skipping 32 matching lines @@
     auto it = m_stateForPointer.find(event.pointer);
     if (it == m_stateForPointer.end())
         return false;
     PointerState stateCopy = it->second;
     m_stateForPointer.erase(it);
     ASSERT(stateCopy.target);
     return dispatchPointerEvent(stateCopy, event);
 }
 
 }