Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/dom_distiller/ReaderModePanel.java

Index: chrome/android/java_staging/src/org/chromium/chrome/browser/dom_distiller/ReaderModePanel.java
diff --git a/chrome/android/java_staging/src/org/chromium/chrome/browser/dom_distiller/ReaderModePanel.java b/chrome/android/java_staging/src/org/chromium/chrome/browser/dom_distiller/ReaderModePanel.java
new file mode 100644
index 0000000000000000000000000000000000000000..aa4c6cce7d68fe7ba640a8bec8464de17e519902
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+++ b/chrome/android/java_staging/src/org/chromium/chrome/browser/dom_distiller/ReaderModePanel.java
@@ -0,0 +1,682 @@
+// 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.
+
+package org.chromium.chrome.browser.dom_distiller;
+
+import static org.chromium.chrome.browser.compositor.layouts.ChromeAnimation.AnimatableAnimation.createAnimation;
+
+import android.content.Context;
+
+import org.chromium.base.metrics.RecordUserAction;
+import org.chromium.chrome.browser.ContentViewUtil;
+import org.chromium.chrome.browser.Tab;
+import org.chromium.chrome.browser.compositor.layouts.ChromeAnimation;
+import org.chromium.chrome.browser.compositor.layouts.ChromeAnimation.Animatable;
+import org.chromium.chrome.browser.compositor.layouts.eventfilter.EdgeSwipeEventFilter.ScrollDirection;
+import org.chromium.chrome.browser.dom_distiller.ReaderModeButtonView.ReaderModeButtonViewDelegate;
+import org.chromium.chrome.browser.tab.ChromeTab;
+import org.chromium.chrome.browser.util.MathUtils;
+import org.chromium.content.browser.ContentView;
+import org.chromium.content.browser.ContentViewCore;
+import org.chromium.content_public.browser.WebContentsObserver;
+import org.chromium.content_public.common.TopControlsState;
+import org.chromium.ui.base.WindowAndroid;
+
+/**
+ * Manages UI effects for reader mode including hiding and showing the
+ * reader mode and reader mode preferences toolbar icon and hiding the
+ * top controls when a reader mode page has finished loading.
+ *
+ * TODO(aruslan): combine with ContextualSearchPanel.
+ */
+public class ReaderModePanel implements ChromeAnimation.Animatable<ReaderModePanel.Property> {
+    // TODO(aruslan): pull this from the FullscreenManager.
+    private static final float TOOLBAR_HEIGHT_DP = 56.0f;
+
+    private static final float PANEL_HEIGHT_DP = TOOLBAR_HEIGHT_DP;
+    private static final float SHADOW_HEIGHT_DP = 4.0f;
+    private static final float MINIMAL_BORDER_X_DP = 4.0f;
+    private static final float DARKEN_LAYOUTTAB_BRIGHTNESS = 0.3f;
+    private static final float MAX_LAYOUTTAB_DISPLACEMENT = 3.0f * TOOLBAR_HEIGHT_DP;
+
+    private static final float SNAP_BACK_THRESHOLD = 0.3f;
+    private static final long BASE_ANIMATION_DURATION_MS = 500;
+
+    /**
+     * Panel's host interface.
+     */
+    public interface ReaderModePanelHost {
+        /**
+         * @return Whether the reader mode button should be animated.
+         */
+        boolean allowReaderModeButtonAnimation();
+
+        /**
+         * @return Reader mode header background color.
+         */
+        int getReaderModeHeaderBackgroundColor();
+
+        /**
+         * @return One of ReaderModeManager.POSSIBLE, NOT_POSSIBLE, STARTED constants.
+         */
+        int getReaderModeStatus();
+
+        /**
+         * @return An associated tab.
+         */
+        Tab getTab();
+
+        /**
+         * @param X X-coordinate in dp
+         * @param Y Y-coordinate in dp
+         * @return Whether a given coordinates are within the bounds of the "dismiss" button
+         */
+        public boolean isInsideDismissButton(float x, float y);
+    }
+
+    /**
+     * Layout integration interface.
+     */
+    public interface ReaderModePanelLayoutDelegate {
+        /**
+         * Requests a next update to refresh the transforms and changing properties.
+         */
+        void requestUpdate();
+
+        /**
+         * Sets the brightness of the LayoutTab to a given value.
+         * @param v Brightness
+         */
+        void setLayoutTabBrightness(float v);
+
+        /**
+         * Sets the Y offset of the LayoutTab to a given value.
+         * @param v Y-offset in dp
+         */
+        void setLayoutTabY(float v);
+    }
+
+    /**
+     * Properties that can be animated by using a
+     * {@link org.chromium.chrome.browser.compositor.layouts.ChromeAnimation.Animatable}.
+     */
+    public enum Property {
+        /**
+         * Parametric vertical slider from
+         * -1.0 (panel is out of screen) to
+         * 0.0 (panel is on screen) to
+         * 1.0 (panel covers the entire screen)
+         */
+        SLIDING_T,
+        /**
+         * Horizontal slider, offset in dp
+         */
+        X,
+    }
+
+    private float mSlidingT;
+    private float mX;
+
+    private ScrollDirection mSwipeDirection;  // set in swipeStarted
+    private float mInitialPanelDistanceFromBottom;  // distance from the bottom at swipeStarted
+    private float mInitialX;  // X at swipeStarted
+
+    /**
+     * The animation set.
+     */
+    private ChromeAnimation<ChromeAnimation.Animatable<?>> mLayoutAnimations;
+
+    private boolean mIsReaderModePanelHidden;
+    private boolean mIsReaderModePanelDismissed;
+    private ContentViewCore mDistilledContentViewCore;
+    private WebContentsObserver mDistilledContentObserver;
+    private boolean mDidFirstNonEmptyDistilledPaint;
+    private ReaderModePanelLayoutDelegate mLayoutDelegate;
+
+    private float mLayoutWidth;
+    private float mLayoutHeight;
+    private boolean mIsToolbarShowing;
+    private float mDpToPx;
+
+    /**
+     * The {@link ReaderModePanelHost} used to get reader mode status and the associated tab.
+     */
+    private final ReaderModePanelHost mReaderModeHost;
+
+    /**
+     * Non-animated button support.
+     */
+    private boolean mAllowAnimatedButton;
+    private ReaderModeButtonView mReaderModeButtonView;
+
+    public ReaderModePanel(ReaderModePanelHost readerModeHost) {
+        mReaderModeHost = readerModeHost;
+        mAllowAnimatedButton = mReaderModeHost.allowReaderModeButtonAnimation();
+
+        mLayoutWidth = 0.0f;
+        mLayoutHeight = 0.0f;
+        mDpToPx = 1.0f;
+
+        mSlidingT = -1.0f;
+        mX = 0.0f;
+    }
+
+    /**
+     * Destroys the panel and associated resources.
+     */
+    public void onDestroy() {
+        mLayoutAnimations = null;
+        hideButtonBar();
+    }
+
+    /**
+     * Set the layout delegate.
+     * @param layoutDelegate A {@link ReaderModePanelLayoutDelegate} to call.
+     */
+    public void setLayoutDelegate(ReaderModePanelLayoutDelegate layoutDelegate) {
+        mLayoutDelegate = layoutDelegate;
+        requestUpdate();
+    }
+
+    // ChromeAnimation.Animatable<Property>:
+
+    private void setSlidingT(float val) {
+        mSlidingT = val;
+        if (mLayoutDelegate != null) {
+            mLayoutDelegate.setLayoutTabBrightness(getTabBrightness());
+            mLayoutDelegate.setLayoutTabY(getTabYOffset());
+        }
+    }
+
+    @Override
+    public void setProperty(Property prop, float val) {
+        switch (prop) {
+            case SLIDING_T:
+                setSlidingT(val);
+                break;
+            case X:
+                mX = val;
+                break;
+        }
+    }
+
+    private static float clamp(float val, float lower, float higher) {
+        return val < lower ? lower : (val > higher ? higher : val);
+    }
+
+    private static float interp(float factor, float start, float end) {
+        return start + clamp(factor, 0.0f, 1.0f) * (end - start);
+    }
+
+    private float getPanelDistanceFromBottom() {
+        if (mSlidingT < 0.0f) return interp(mSlidingT + 1.0f, 0.0f, PANEL_HEIGHT_DP);
+        return PANEL_HEIGHT_DP + interp(mSlidingT, 0.0f, getFullscreenHeight());
+    }
+
+    private float getSlidingTForPanelDistanceFromBottom(float distanceFromBottom) {
+        if (distanceFromBottom >= PANEL_HEIGHT_DP) {
+            return interp(
+                    (distanceFromBottom - PANEL_HEIGHT_DP) / getFullscreenHeight(),
+                    0.0f, 1.0f);
+        }
+        return interp(
+                (PANEL_HEIGHT_DP - distanceFromBottom) / PANEL_HEIGHT_DP,
+                0.0f, -1.0f);
+    }
+
+    private float getDistilledContentDistanceFromBottom() {
+        if (mSlidingT < 0.0f) return interp(mSlidingT + 1.0f, -PANEL_HEIGHT_DP, 0.0f);
+        return interp(mSlidingT, 0.0f, getFullscreenHeight());
+    }
+
+    private static float snapBackSlidingT(float v) {
+        // We snap asymmetrically: 30% is enough to get it opened, but 70% is necessary to dismiss.
+        v = (v < -1.0f + SNAP_BACK_THRESHOLD) ? v : (v >= SNAP_BACK_THRESHOLD ? v : 0.0f);
+        return Math.signum(v);
+    }
+
+    private static float snapBackX(float v) {
+        // Horizontally we snap symmetrically: more than 70% to each side to dismiss.
+        v = (v < -1.0f + SNAP_BACK_THRESHOLD) ? v : (v >= 1.0f - SNAP_BACK_THRESHOLD ? v : 0.0f);
+        return Math.signum(v);
+    }
+
+    // Gesture handling:
+
+    /**
+     * @param direction Swipe direction to test
+     * @return Whether the swipe in a given direction is enabled
+     */
+    public boolean isSwipeEnabled(ScrollDirection direction) {
+        return !isAnimating();
+    }
+
+    /**
+     * Called when the swipe is started.
+     * @param direction Swipe direction
+     * @param x X-coordinate of the starting point in dp
+     * @param y Y-coordinate of the starting point in dp
+     */
+    public void swipeStarted(ScrollDirection direction, float x, float y) {
+        if (isAnimating()) return;
+
+        mSwipeDirection = direction;
+        mInitialPanelDistanceFromBottom = getPanelDistanceFromBottom();
+        mX = getX();
+
+        if (mSwipeDirection == ScrollDirection.UP) activatePreviewOfDistilledMode();
+
+        requestUpdate();
+    }
+
+    /**
+     * Called when the swipe is continued.
+     * @param tx X-offset since the start of the swipe in dp
+     * @param ty Y-offset since the start of the swipe in dp
+     */
+    public void swipeUpdated(float x, float y, float dx, float dy, float tx, float ty) {
+        if (isAnimating()) return;
+
+        if (mSwipeDirection == ScrollDirection.LEFT || mSwipeDirection == ScrollDirection.RIGHT) {
+            setProperty(ReaderModePanel.Property.X, clamp(mInitialX + tx,
+                    -mLayoutWidth + MINIMAL_BORDER_X_DP, mLayoutWidth - MINIMAL_BORDER_X_DP));
+        } else {
+            setProperty(ReaderModePanel.Property.SLIDING_T,
+                    getSlidingTForPanelDistanceFromBottom(mInitialPanelDistanceFromBottom - ty));
+        }
+        requestUpdate();
+    }
+
+    /**
+     * Called when the swipe is finished.
+     */
+    public void swipeFinished() {
+        if (isAnimating()) return;
+
+        final float snappedX = snapBackX(mX / mLayoutWidth) * mLayoutWidth;
+        final float snappedSlidingT = snapBackSlidingT(mSlidingT);
+        if (snappedX <= -mLayoutWidth || snappedX >= mLayoutWidth) dismissButtonBar();
+        if (snappedSlidingT < 0.0f) dismissButtonBar();
+
+        animateTo(snappedX, snappedSlidingT, true);
+    }
+
+    // Panel layout handling:
+
+    /**
+     * @return Whether the panel should be shown.
+     */
+    public boolean isShowing() {
+        return isPanelWithinScreenBounds() || isAnimating() || mDistilledContentViewCore != null;
+    }
+
+    /**
+     * @return Whether the panel is within screen bounds.
+     */
+    private boolean isPanelWithinScreenBounds() {
+        return mSlidingT > -1.0f;
+    }
+
+    /**
+     * @return The fullscreen height.
+     */
+    private float getFullscreenHeight() {
+        return mLayoutHeight + TOOLBAR_HEIGHT_DP;
+    }
+
+    public float getFullscreenY(float y) {
+        if (mIsToolbarShowing) y += TOOLBAR_HEIGHT_DP * mDpToPx;
+        return y;
+    }
+
+    public float getPanelY() {
+        return getFullscreenHeight() - getPanelDistanceFromBottom() - SHADOW_HEIGHT_DP;
+    }
+
+    public float getDistilledContentY() {
+        return getFullscreenHeight() - getDistilledContentDistanceFromBottom() - SHADOW_HEIGHT_DP;
+    }
+
+    public float getWidth() {
+        return mLayoutWidth;
+    }
+
+    public float getPanelHeight() {
+        return getPanelDistanceFromBottom();
+    }
+
+    public float getMarginTop() {
+        return SHADOW_HEIGHT_DP;
+    }
+
+    public float getDistilledHeight() {
+        return getDistilledContentDistanceFromBottom();
+    }
+
+    public float getX() {
+        return mX;
+    }
+
+    public float getTextOpacity() {
+        return interp(mSlidingT, 1.0f, 0.0f);
+    }
+
+    public float getTabBrightness() {
+        return interp(mSlidingT, 1.0f, DARKEN_LAYOUTTAB_BRIGHTNESS);
+    }
+
+    public float getTabYOffset() {
+        return interp(mSlidingT, 0.0f, -MAX_LAYOUTTAB_DISPLACEMENT);
+    }
+
+    /**
+     * @param currentOffset The current top controls offset in dp.
+     * @return {@link Float#NaN} if no offset should be used, or a value in dp
+     *         if the top controls offset should be overridden.
+     */
+    public float getTopControlsOffset(float currentOffsetDp) {
+        if (mSlidingT <= 0.0f) return Float.NaN;
+        return MathUtils.clamp(getTabYOffset(), -TOOLBAR_HEIGHT_DP, Math.min(currentOffsetDp, 0f));
+    }
+
+
+    public ContentViewCore getDistilledContentViewCore() {
+        return mDistilledContentViewCore;
+    }
+
+    public boolean didFirstNonEmptyDistilledPaint() {
+        return mDidFirstNonEmptyDistilledPaint;
+    }
+
+    public int getReaderModeHeaderBackgroundColor() {
+        return mReaderModeHost.getReaderModeHeaderBackgroundColor();
+    }
+
+    /**
+     * Called when the size of the view has changed.
+     *
+     * @param width  The new width in dp.
+     * @param height The new width in dp.
+     * @param isToolbarShowing Whether the Toolbar is showing.
+     * @param dpToPx Multipler to convert from dp to pixels.
+     */
+    public void onSizeChanged(float width, float height, boolean isToolbarShowing, float dpToPx) {
+        mLayoutWidth = width;
+        mLayoutHeight = height;
+        mIsToolbarShowing = isToolbarShowing;
+        mDpToPx = dpToPx;
+    }
+
+    // Layout integration:
+
+    /**
+     * Requests a new frame to be updated and rendered.
+     */
+    private void requestUpdate() {
+        if (mLayoutDelegate != null) mLayoutDelegate.requestUpdate();
+    }
+
+    // Animation handling:
+
+    /**
+     * @return Whether a panel animation is in progress.
+     */
+    private boolean isAnimating() {
+        return mLayoutAnimations != null && !mLayoutAnimations.finished();
+    }
+
+    /**
+     * Animates to a given target value.
+     * @param targetX A target value for the X parameter
+     * @param targetSlidingT A target value for the SlidingT parameter
+     */
+    private void animateTo(float targetX, float targetSlidingT, boolean animate) {
+        if (targetSlidingT > 0.0f) activatePreviewOfDistilledMode();
+
+        if (isAnimating()) {
+            mLayoutAnimations.cancel(this, Property.SLIDING_T);
+            mLayoutAnimations.cancel(this, Property.X);
+        }
+        if (mLayoutAnimations == null || mLayoutAnimations.finished()) {
+            mLayoutAnimations = new ChromeAnimation<Animatable<?>>();
+        }
+
+        mLayoutAnimations.add(createAnimation(
+                this, Property.SLIDING_T, mSlidingT, targetSlidingT,
+                BASE_ANIMATION_DURATION_MS, 0, false,
+                ChromeAnimation.getDecelerateInterpolator()));
+        mLayoutAnimations.add(createAnimation(
+                this, Property.X, mX, targetX,
+                BASE_ANIMATION_DURATION_MS, 0, false,
+                ChromeAnimation.getDecelerateInterpolator()));
+        mLayoutAnimations.start();
+
+        if (!animate) mLayoutAnimations.updateAndFinish();
+        requestUpdate();
+    }
+
+    /**
+     * Steps the animation forward and updates all the animated values.
+     * @param time      The current time of the app in ms.
+     * @param jumpToEnd Whether to finish the animation.
+     * @return          Whether the animation was finished.
+     */
+    public boolean onUpdateAnimation(long time, boolean jumpToEnd) {
+        boolean finished = true;
+        if (mLayoutAnimations != null) {
+            if (jumpToEnd) {
+                finished = mLayoutAnimations.finished();
+                mLayoutAnimations.updateAndFinish();
+            } else {
+                finished = mLayoutAnimations.update(time);
+            }
+
+            if (finished || jumpToEnd) {
+                mLayoutAnimations = null;
+                onAnimationFinished();
+            }
+            requestUpdate();
+        }
+        return finished;
+    }
+
+    /**
+     * Called when layout-specific actions are needed after the animation finishes.
+     */
+    private void onAnimationFinished() {
+        if (mSlidingT >= 1.0f) enterDistilledMode();
+        updateBottomButtonBar();
+    }
+
+    // Gesture handling:
+
+    /**
+     * @param y The y coordinate in dp.
+     * @return Whether the given |y| coordinate is inside the Reader mode area.
+     */
+    public boolean isYCoordinateInsideReaderModePanel(float y) {
+        return y >= getPanelY() || y >= getDistilledContentY();
+    }
+
+    /**
+     * Handles a click in the panel area.
+     * @param x X-coordinate in dp
+     * @param y Y-coordinate in dp
+     */
+    public void handleClick(long time, float x, float y) {
+        if (mReaderModeHost.isInsideDismissButton(x * mDpToPx + mX, PANEL_HEIGHT_DP / 2)) {
+            dismissButtonBar();
+            return;
+        }
+
+        animateTo(mX, 1.0f, true);
+    }
+
+    private void nonAnimatedUpdateButtomButtonBar() {
+        final int status = mReaderModeHost.getReaderModeStatus();
+        final Tab tab = mReaderModeHost.getTab();
+
+        if (mReaderModeButtonView != null
+                && (status != ReaderModeManager.POSSIBLE || mIsReaderModePanelHidden
+                        || mIsReaderModePanelDismissed)) {
+            mReaderModeButtonView.dismiss(true);
+            mReaderModeButtonView = null;
+            return;
+        }
+        if (mReaderModeButtonView == null
+                && (status == ReaderModeManager.POSSIBLE && !mIsReaderModePanelHidden
+                        && !mIsReaderModePanelDismissed)) {
+            mReaderModeButtonView = ReaderModeButtonView.create(tab.getContentViewCore(),
+                    new ReaderModeButtonViewDelegate() {
+                        @Override
+                        public void onSwipeAway() {
+                            dismissButtonBar();
+                        }
+
+                        @Override
+                        public void onClick() {
+                            nonAnimatedEnterDistilledMode();
+                        }
+                    });
+        }
+    }
+
+    /**
+     * Updates the visibility of the reader mode button bar as required.
+     */
+    public void updateBottomButtonBar() {
+        if (!mAllowAnimatedButton) {
+            nonAnimatedUpdateButtomButtonBar();
+            return;
+        }
+
+        if (isAnimating()) return;
+
+        final int status = mReaderModeHost.getReaderModeStatus();
+        if (isPanelWithinScreenBounds()
+                && (status != ReaderModeManager.POSSIBLE
+                        || mIsReaderModePanelHidden || mIsReaderModePanelDismissed)) {
+            animateTo(0.0f, -1.0f, true);
+            destroyDistilledContentViewCore();
+            requestUpdate();
+            return;
+        }
+
+        if (!isPanelWithinScreenBounds()
+                && (status == ReaderModeManager.POSSIBLE
+                        && !mIsReaderModePanelHidden && !mIsReaderModePanelDismissed)) {
+            animateTo(0.0f, 0.0f, true);
+            requestUpdate();
+            return;
+        }
+    }
+
+    private static ContentViewCore createDistillerContentViewCore(
+            Context context, WindowAndroid windowAndroid) {
+        ContentViewCore cvc = new ContentViewCore(context);
+        ContentView cv = new ContentView(context, cvc);
+        cvc.initialize(cv, cv, ContentViewUtil.createWebContents(false, true), windowAndroid);
+        return cvc;
+    }
+
+    /**
+     * Prepares the distilled mode.
+     */
+    public void activatePreviewOfDistilledMode() {
+        if (mDistilledContentViewCore != null) return;
+
+        mDidFirstNonEmptyDistilledPaint = false;
+        mDistilledContentViewCore = createDistillerContentViewCore(
+                mReaderModeHost.getTab().getContentViewCore().getContext(),
+                mReaderModeHost.getTab().getWindowAndroid());
+        mDistilledContentObserver = new WebContentsObserver(
+                mDistilledContentViewCore.getWebContents()) {
+            @Override
+            public void didFirstVisuallyNonEmptyPaint() {
+                super.didFirstVisuallyNonEmptyPaint();
+                mDidFirstNonEmptyDistilledPaint = true;
+            }
+        };
+        mReaderModeHost.getTab().attachOverlayContentViewCore(
+                mDistilledContentViewCore, true, false);
+        DomDistillerTabUtils.distillAndView(
+                mReaderModeHost.getTab().getContentViewCore().getWebContents(),
+                mDistilledContentViewCore.getWebContents());
+        mDistilledContentViewCore.onShow();
+
+        mReaderModeHost.getTab().updateTopControlsState(TopControlsState.BOTH, false);
+    }
+
+    private void nonAnimatedEnterDistilledMode() {
+        RecordUserAction.record("DomDistiller_DistilledPageOpened");
+        DomDistillerTabUtils.distillCurrentPageAndView(mReaderModeHost.getTab().getWebContents());
+        mReaderModeHost.getTab().updateTopControlsState(TopControlsState.SHOWN, false);
+        nonAnimatedUpdateButtomButtonBar();
+    }
+
+    private void enterDistilledMode() {
+        RecordUserAction.record("DomDistiller_DistilledPageOpened");
+        mSlidingT = -1.0f;
+        requestUpdate();
+
+        mReaderModeHost.getTab().updateTopControlsState(TopControlsState.HIDDEN, false);
+        DomDistillerTabUtils.distillCurrentPageAndView(mReaderModeHost.getTab().getWebContents());
+        destroyDistilledContentViewCore();
+        if (mLayoutDelegate != null) {
+            mLayoutDelegate.setLayoutTabBrightness(1.0f);
+            mLayoutDelegate.setLayoutTabY(0.0f);
+        }
+
+        updateBottomButtonBar();
+    }
+
+    private void destroyDistilledContentViewCore() {
+        if (mDistilledContentViewCore == null) return;
+
+        mDistilledContentObserver.destroy();
+        mDistilledContentObserver = null;
+        mReaderModeHost.getTab().detachOverlayContentViewCore(mDistilledContentViewCore);
+        mDistilledContentViewCore.destroy();
+        mDistilledContentViewCore = null;
+    }
+
+    /**
+     * Hides the reader mode button bar if shown.
+     */
+    public void hideButtonBar() {
+        if (mIsReaderModePanelHidden) return;
+
+        mIsReaderModePanelHidden = true;
+        updateBottomButtonBar();
+    }
+
+    /**
+     * Dismisses the reader mode button bar if shown.
+     */
+    public void dismissButtonBar() {
+        if (mIsReaderModePanelDismissed) return;
+
+        mIsReaderModePanelDismissed = true;
+        updateBottomButtonBar();
+    }
+
+    /**
+     * Shows the reader mode button bar if necessary.
+     */
+    public void unhideButtonBar() {
+        mIsReaderModePanelHidden = false;
+        updateBottomButtonBar();
+    }
+
+    /**
+      * @param tab A {@link Tab}.
+      * @return The panel associated with a given Tab.
+      */
+    public static ReaderModePanel getReaderModePanel(Tab tab) {
+        if (!(tab instanceof ChromeTab)) return null;
+        ReaderModeManager manager = ((ChromeTab) tab).getReaderModeManager();
+        if (manager == null) return null;
+        return manager.getReaderModePanel();
+    }
+}