diff -r 000000000000 -r 6474c204b198 gfx/layers/apz/util/ActiveElementManager.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/layers/apz/util/ActiveElementManager.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,153 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ActiveElementManager.h"
+#include "mozilla/EventStates.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "inIDOMUtils.h"
+#include "nsIDOMDocument.h"
+#include "nsIDOMElement.h"
+#include "nsIDOMEventTarget.h"
+#include "base/message_loop.h"
+#include "base/task.h"
+
+namespace mozilla {
+namespace layers {
+
+static int32_t sActivationDelayMs = 100;
+static bool sActivationDelayMsSet = false;
+
+ActiveElementManager::ActiveElementManager()
+  : mDomUtils(services::GetInDOMUtils()),
+    mCanBePan(false),
+    mCanBePanSet(false),
+    mSetActiveTask(nullptr)
+{
+  if (!sActivationDelayMsSet) {
+    Preferences::AddIntVarCache(&sActivationDelayMs,
+                                "ui.touch_activation.delay_ms",
+                                sActivationDelayMs);
+    sActivationDelayMsSet = true;
+  }
+}
+
+ActiveElementManager::~ActiveElementManager() {}
+
+void
+ActiveElementManager::SetTargetElement(nsIDOMEventTarget* aTarget)
+{
+  if (mTarget) {
+    // Multiple fingers on screen (since HandleTouchEnd clears mTarget).
+    CancelTask();
+    ResetActive();
+    mTarget = nullptr;
+    return;
+  }
+
+  mTarget = do_QueryInterface(aTarget);
+  TriggerElementActivation();
+}
+
+void
+ActiveElementManager::HandleTouchStart(bool aCanBePan)
+{
+  mCanBePan = aCanBePan;
+  mCanBePanSet = true;
+  TriggerElementActivation();
+}
+
+void
+ActiveElementManager::TriggerElementActivation()
+{
+  // Both HandleTouchStart() and SetTargetElement() call this. They can be
+  // called in either order. One will set mCanBePanSet, and the other, mTarget.
+  // We want to actually trigger the activation once both are set.
+  if (!(mTarget && mCanBePanSet)) {
+    return;
+  }
+
+  // If the touch cannot be a pan, make mTarget :active right away.
+  // Otherwise, wait a bit to see if the user will pan or not.
+  if (!mCanBePan) {
+    SetActive(mTarget);
+  } else {
+    mSetActiveTask = NewRunnableMethod(
+        this, &ActiveElementManager::SetActiveTask, mTarget);
+    MessageLoop::current()->PostDelayedTask(
+        FROM_HERE, mSetActiveTask, sActivationDelayMs);
+  }
+}
+
+void
+ActiveElementManager::HandlePanStart()
+{
+  // The user started to pan, so we don't want mTarget to be :active.
+  // Make it not :active, and clear any pending task to make it :active.
+  CancelTask();
+  ResetActive();
+}
+
+void
+ActiveElementManager::HandleTouchEnd(bool aWasClick)
+{
+  // If the touch was a click, make mTarget :active right away.
+  // nsEventStateManager will reset the active element when processing
+  // the mouse-down event generated by the click.
+  CancelTask();
+  if (aWasClick) {
+    SetActive(mTarget);
+  }
+
+  // Clear mTarget for next touch.
+  mTarget = nullptr;
+}
+
+void
+ActiveElementManager::SetActive(nsIDOMElement* aTarget)
+{
+  if (mDomUtils) {
+    mDomUtils->SetContentState(aTarget, NS_EVENT_STATE_ACTIVE.GetInternalValue());;
+  }
+}
+
+void
+ActiveElementManager::ResetActive()
+{
+  // Clear the :active flag from mTarget by setting it on the document root.
+  if (mTarget) {
+    nsCOMPtr<nsIDOMDocument> doc;
+    mTarget->GetOwnerDocument(getter_AddRefs(doc));
+    if (doc) {
+      nsCOMPtr<nsIDOMElement> root;
+      doc->GetDocumentElement(getter_AddRefs(root));
+      if (root) {
+        SetActive(root);
+      }
+    }
+  }
+}
+
+void
+ActiveElementManager::SetActiveTask(nsIDOMElement* aTarget)
+{
+  // This gets called from mSetActiveTask's Run() method. The message loop
+  // deletes the task right after running it, so we need to null out
+  // mSetActiveTask to make sure we're not left with a dangling pointer.
+  mSetActiveTask = nullptr;
+  SetActive(aTarget);
+}
+
+void
+ActiveElementManager::CancelTask()
+{
+  if (mSetActiveTask) {
+    mSetActiveTask->Cancel();
+    mSetActiveTask = nullptr;
+  }
+}
+
+}
+}