diff -r 000000000000 -r 6474c204b198 mobile/android/base/DynamicToolbar.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/DynamicToolbar.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,167 @@
+package org.mozilla.gecko;
+
+import java.util.EnumSet;
+
+import org.mozilla.gecko.PrefsHelper.PrefHandlerBase;
+import org.mozilla.gecko.gfx.LayerView;
+import org.mozilla.gecko.util.ThreadUtils;
+
+import android.os.Bundle;
+
+public class DynamicToolbar {
+    private static final String STATE_ENABLED = "dynamic_toolbar";
+    private static final String CHROME_PREF = "browser.chrome.dynamictoolbar";
+
+    // DynamicToolbar is enabled iff prefEnabled is true *and* accessibilityEnabled is false,
+    // so it is disabled by default on startup. We do not enable it until we explicitly get
+    // the pref from Gecko telling us to turn it on.
+    private volatile boolean prefEnabled;
+    private boolean accessibilityEnabled;
+
+    private final int prefObserverId;
+    private final EnumSet<PinReason> pinFlags = EnumSet.noneOf(PinReason.class);
+    private LayerView layerView;
+    private OnEnabledChangedListener enabledChangedListener;
+
+    public enum PinReason {
+        RELAYOUT,
+        ACTION_MODE
+    }
+
+    public enum VisibilityTransition {
+        IMMEDIATE,
+        ANIMATE
+    }
+
+    /**
+     * Listener for changes to the dynamic toolbar's enabled state.
+     */
+    public interface OnEnabledChangedListener {
+        /**
+         * This callback is executed on the UI thread.
+         */
+        public void onEnabledChanged(boolean enabled);
+    }
+
+    public DynamicToolbar() {
+        // Listen to the dynamic toolbar pref
+        prefObserverId = PrefsHelper.getPref(CHROME_PREF, new PrefHandler());
+    }
+
+    public void destroy() {
+        PrefsHelper.removeObserver(prefObserverId);
+    }
+
+    public void setLayerView(LayerView layerView) {
+        ThreadUtils.assertOnUiThread();
+
+        this.layerView = layerView;
+    }
+
+    public void setEnabledChangedListener(OnEnabledChangedListener listener) {
+        ThreadUtils.assertOnUiThread();
+
+        enabledChangedListener = listener;
+    }
+
+    public void onSaveInstanceState(Bundle outState) {
+        ThreadUtils.assertOnUiThread();
+
+        outState.putBoolean(STATE_ENABLED, prefEnabled);
+    }
+
+    public void onRestoreInstanceState(Bundle savedInstanceState) {
+        ThreadUtils.assertOnUiThread();
+
+        if (savedInstanceState != null) {
+            prefEnabled = savedInstanceState.getBoolean(STATE_ENABLED);
+        }
+    }
+
+    public boolean isEnabled() {
+        ThreadUtils.assertOnUiThread();
+
+        return prefEnabled && !accessibilityEnabled;
+    }
+
+    public void setAccessibilityEnabled(boolean enabled) {
+        ThreadUtils.assertOnUiThread();
+
+        if (accessibilityEnabled == enabled) {
+            return;
+        }
+
+        // Disable the dynamic toolbar when accessibility features are enabled,
+        // and re-read the preference when they're disabled.
+        accessibilityEnabled = enabled;
+        if (prefEnabled) {
+            triggerEnabledListener();
+        }
+    }
+
+    public void setVisible(boolean visible, VisibilityTransition transition) {
+        ThreadUtils.assertOnUiThread();
+
+        if (layerView == null) {
+            return;
+        }
+
+        final boolean immediate = transition.equals(VisibilityTransition.IMMEDIATE);
+        if (visible) {
+            layerView.getLayerMarginsAnimator().showMargins(immediate);
+        } else {
+            layerView.getLayerMarginsAnimator().hideMargins(immediate);
+        }
+    }
+
+    public void setPinned(boolean pinned, PinReason reason) {
+        ThreadUtils.assertOnUiThread();
+
+        if (layerView == null) {
+            return;
+        }
+
+        if (pinned) {
+            pinFlags.add(reason);
+        } else {
+            pinFlags.remove(reason);
+        }
+
+        layerView.getLayerMarginsAnimator().setMarginsPinned(!pinFlags.isEmpty());
+    }
+
+    private void triggerEnabledListener() {
+        if (enabledChangedListener != null) {
+            enabledChangedListener.onEnabledChanged(isEnabled());
+        }
+    }
+
+    private class PrefHandler extends PrefHandlerBase {
+        @Override
+        public void prefValue(String pref, boolean value) {
+            if (value == prefEnabled) {
+                return;
+            }
+
+            prefEnabled = value;
+
+            ThreadUtils.postToUiThread(new Runnable() {
+                @Override
+                public void run() {
+                    // If accessibility is enabled, the dynamic toolbar is
+                    // forced to be off.
+                    if (!accessibilityEnabled) {
+                        triggerEnabledListener();
+                    }
+                }
+            });
+        }
+
+        @Override
+        public boolean isObserver() {
+            // We want to be notified of changes to be able to switch mode
+            // without restarting.
+            return true;
+        }
+    }
+}
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