Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/tab/BackgroundContentViewHelper.java

Index: chrome/android/java_staging/src/org/chromium/chrome/browser/tab/BackgroundContentViewHelper.java
diff --git a/chrome/android/java_staging/src/org/chromium/chrome/browser/tab/BackgroundContentViewHelper.java b/chrome/android/java_staging/src/org/chromium/chrome/browser/tab/BackgroundContentViewHelper.java
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index 0000000000000000000000000000000000000000..e9c95a3fc1fcaffc33587afe4f5f51424a9bf7e8
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@@ -0,0 +1,897 @@
+// 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.tab;
+
+import android.app.Activity;
+import android.net.Uri;
+import android.os.Handler;
+import android.text.TextUtils;
+
+import org.chromium.base.CalledByNative;
+import org.chromium.base.FieldTrialList;
+import org.chromium.base.metrics.RecordHistogram;
+import org.chromium.base.metrics.RecordUserAction;
+import org.chromium.chrome.browser.ChromeVersionInfo;
+import org.chromium.chrome.browser.ContentViewUtil;
+import org.chromium.chrome.browser.EmptyTabObserver;
+import org.chromium.chrome.browser.Tab;
+import org.chromium.chrome.browser.device.DeviceClassManager;
+import org.chromium.components.web_contents_delegate_android.WebContentsDelegateAndroid;
+import org.chromium.content.browser.ContentView;
+import org.chromium.content.browser.ContentViewClient;
+import org.chromium.content.browser.ContentViewCore;
+import org.chromium.content.browser.RenderCoordinates;
+import org.chromium.content_public.browser.GestureStateListener;
+import org.chromium.content_public.browser.LoadUrlParams;
+import org.chromium.content_public.browser.WebContents;
+import org.chromium.content_public.browser.WebContentsObserver;
+import org.chromium.content_public.common.Referrer;
+import org.chromium.ui.base.WindowAndroid;
+
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Responsible for background content view creation and management.
+ */
+public class BackgroundContentViewHelper extends EmptyTabObserver {
+    private static final String GOOGLE_PREVIEW_SERVER_PREFIX = "icl";
+
+    // Google preview staging and canary servers. Only to be used in dev builds.
+    private static final String GOOGLE_PREVIEW_SERVER_SUFFIX = ".googleusercontent.com";
+
+    private static final String GWS_CHROME_JOINT_EXPERIMENT_ID_STRING = "gcjeid";
+
+    private static final String GOOGLE_DOMAIN_PREFIX = "www.google.";
+
+    // Instant search clicks swap reasons.
+    // IMPORTANT: Do not renumber any existing constants (except the BOUNDARY ones). Keep these in
+    // sync with histograms.xml file.
+    private static final int SWAP_REASON_REGULAR = 0;
+    private static final int SWAP_REASON_TIMEOUT = 1;
+    private static final int SWAP_REASON_ABORT_ON_NAVIGATE = 2;
+    private static final int SWAP_REASON_ON_PREVIEW_FAIL = 3;
+    private static final int SWAP_REASON_ORIGINAL_FAIL = 4;
+    private static final int SWAP_REASON_FORCE = 5;
+    private static final int SWAP_REASON_BOUNDARY = 6;
+
+    // Instant search clicks scroll state while swapping.
+    // IMPORTANT: Do not renumber any existing constants (except the BOUNDARY ones). Keep these in
+    // sync with histograms.xml file.
+    private static final int PREVIEW_SCROLL_STATE_NO_SCROLL = 0;
+    private static final int PREVIEW_SCROLL_STATE_SCROLL = 1;
+    private static final int PREVIEW_SCROLL_STATE_SCROLL_AT_BOTTOM = 2;
+    private static final int PREVIEW_SCROLL_STATE_BOUNDARY = 3;
+
+    // Instant search clicks experiment state.
+    private static final int INSTANT_SEARCH_CLICKS_EXPERIMENT_DISABLED = 0;
+    private static final int INSTANT_SEARCH_CLICKS_EXPERIMENT_ENABLED = 1;
+    private static final int INSTANT_SEARCH_CLICKS_EXPERIMENT_CONTROL = 2;
+
+    /**
+     * The maximum amount of time to wait for the background page to swap. We force the swap after
+     * this timeout.
+     */
+    private final int mSwapTimeoutMs;
+
+    /**
+     * The minimum number of renderer frames needed before swap is triggered.
+     */
+    private final int mMinRendererFramesNeededForSwap;
+
+    // Native pointer corresponding to the current object.
+    private long mNativeBackgroundContentViewHelperPtr;
+
+    // The content view core created to load url in background.
+    private ContentViewCore mContentViewCore;
+
+    // Android window used to created content view.
+    private final WindowAndroid mWindowAndroid;
+
+    // The webcontents observer on current content view of the tab.
+    private WebContentsObserver mCurrentViewWebContentsObserver;
+
+    // The webcontents observer that listens for events to swap in the new WebContents.
+    private WebContentsObserver mWebContentsObserver;
+
+    // The webcontents delegate that gets notified when background view is ready to be swapped.
+    private final WebContentsDelegateAndroid mWebContentsDelegate;
+
+    // Whether or not the preview page finished loading.
+    private boolean mPreviewLoaded = false;
+
+    // Whether or not the background view has painted anything non-empty.
+    private boolean mPaintedNonEmpty = false;
+
+    private int mNumRendererFramesReceived = 0;
+
+    // Whether or not the swap is in progress. We will be in this state while syncing scroll offsets
+    // between content views.
+    private boolean mSwapInProgress = false;
+
+    // Whether or not the background view started loading content.
+    private boolean mDidStartLoad = false;
+
+    // Whether or not the background view finished loading.
+    private boolean mDidFinishLoad = false;
+
+    // The tab associated with the background view.
+    private final Tab mTab;
+
+    // The delegate who is notified when background content view is ready.
+    private final BackgroundContentViewDelegate mDelegate;
+
+    // GestureStateListener attached to the background contentView.
+    private final GestureStateListener mBackgroundGestureStateListener;
+
+    // GestureStateListener attached to the current contentView of tab.
+    private final GestureStateListener mCurrentViewGestureStateListener;
+
+    private final Handler mHandler;
+
+    private final Runnable mSwapOnTimeout = new Runnable() {
+        @Override
+        public void run() {
+            forceSwappingContentViews();
+            RecordHistogram.recordEnumeratedHistogram(
+                    "InstantSearchClicks.ReasonForSwap",
+                    SWAP_REASON_TIMEOUT, SWAP_REASON_BOUNDARY);
+        }
+    };
+
+    private long mBackgroundLoadStartTimeStampMs;
+
+    /**
+     * Whether or not to record 'instant search clicks' uma for the current loaded page in tab.
+     * This is set to true, for instant search clicks enabled urls(preview urls) and also for the
+     * 'would have been' instant search click enabled urls.
+     */
+    private boolean mRecordUma = false;
+
+    private final int mExperimentGroup;
+
+    /**
+     * The recent load progress before swapping. This will be used to return the progress after
+     * swapping the page views.
+     */
+    private int mLoadProgress;
+
+    /**
+     * Whether we transferred pagescale from preview to original.
+     */
+    private boolean mOriginalPageZoomed = false;
+
+    /**
+     * The delegate that is notified when BackgroundContentView is ready to be swapped in.
+     */
+    public interface BackgroundContentViewDelegate {
+        /**
+         * Called when the background content view has drawn non-empty screen..
+         * @param cvc The background ContentViewCore that is ready to be swapped in.
+         * @param didStartLoad  Whether WebContentsObserver::DidStartProvisionalLoadForFrame() has
+         *                      been called for background ContentViewCore.
+         * @param didFinishLoad Whether WebContentsObserver::DidFinishLoad() has already been
+         *                      called for background {@link ContentViewCore}.
+         * @param progress      The recent load progress that was received for the
+         *                      {@link ContentView}.
+         */
+        void onBackgroundViewReady(
+                ContentViewCore cvc, boolean didStartLoad, boolean didFinishLoad, int progress);
+
+        /**
+         * Called to notify the load progress of backgrounc content view.
+         * @param progress      The recent load progress that was received for the
+         *                      {@link ContentView}.
+         */
+        void onLoadProgressChanged(int progress);
+    }
+
+    /**
+     * Creates an instance of BackgroundContentViewHelper.
+     * @param window    An instance of a {@link WindowAndroid}.
+     * @param tab       The {@link ChromeTab} associated with current backgruond view.
+     * @param delegate  The {@link BackgroundContentViewDelegate} to notify when backgruond view is
+     *                  ready to swap in.
+     */
+    public BackgroundContentViewHelper(WindowAndroid windowAndroid, Tab tab,
+            BackgroundContentViewDelegate delegate) {
+        mWindowAndroid = windowAndroid;
+        mNativeBackgroundContentViewHelperPtr = nativeInit();
+
+        mTab = tab;
+        assert delegate != null;
+        mDelegate = delegate;
+        mTab.addObserver(this);
+        mBackgroundGestureStateListener = new GestureStateListener() {
+            @Override
+            public void onScrollOffsetOrExtentChanged(int scrollOffsetY, int scrollExtentY) {
+                syncPageStateAndSwapIfReady();
+            }
+        };
+
+        mCurrentViewGestureStateListener = new GestureStateListener() {
+            @Override
+            public void onFlingEndGesture(int scrollOffsetY, int scrollExtentY) {
+                syncPageStateAndSwapIfReady();
+            }
+
+            @Override
+            public void onScrollEnded(int scrollOffsetY, int scrollExtentY) {
+                syncPageStateAndSwapIfReady();
+            }
+
+            @Override
+            public void onSingleTap(boolean consumed, int x, int y) {
+                recordSingleTap();
+            }
+        };
+
+        mWebContentsDelegate = new WebContentsDelegateAndroid() {
+            @Override
+            public void onLoadProgressChanged(int progress) {
+                mLoadProgress = progress;
+                mDelegate.onLoadProgressChanged(progress);
+                trySwappingBackgroundView();
+            }
+        };
+        mHandler = new Handler();
+
+        mSwapTimeoutMs = nativeGetSwapTimeoutMs(mNativeBackgroundContentViewHelperPtr);
+        mMinRendererFramesNeededForSwap =
+            nativeGetNumFramesNeededForSwap(mNativeBackgroundContentViewHelperPtr);
+        mBackgroundLoadStartTimeStampMs = System.currentTimeMillis();
+        mExperimentGroup = getExperimentGroup();
+    }
+
+    /*
+     * @return Experiment group that the current user fall into.
+     */
+    private int getExperimentGroup() {
+        if (!DeviceClassManager.enableInstantSearchClicks()) {
+            return INSTANT_SEARCH_CLICKS_EXPERIMENT_DISABLED;
+        }
+
+        String instantSearchClicksFieldTrialValue =
+                FieldTrialList.findFullName("InstantSearchClicks");
+        if (TextUtils.equals(instantSearchClicksFieldTrialValue, "Enabled")
+                || TextUtils.equals(instantSearchClicksFieldTrialValue,
+                        "InstantSearchClicksEnabled")) {
+            return INSTANT_SEARCH_CLICKS_EXPERIMENT_ENABLED;
+        } else if (TextUtils.equals(instantSearchClicksFieldTrialValue, "Control")) {
+            return INSTANT_SEARCH_CLICKS_EXPERIMENT_CONTROL;
+        }
+        return INSTANT_SEARCH_CLICKS_EXPERIMENT_DISABLED;
+    }
+
+    /**
+     * @return True iff content height of original page is greater than preview page.
+     */
+    private boolean hasBackgroundPageLoadedMoreThanPreview() {
+        if (!mPaintedNonEmpty || mTab.getContentViewCore() == null) return false;
+        return getContentViewCore().getContentHeightCss()
+                > mTab.getContentViewCore().getContentHeightCss();
+    }
+
+    /**
+     * @return True iff original page is loading in background content view which is not swapped in.
+     */
+    public boolean hasPendingBackgroundPage() {
+        return mContentViewCore != null;
+    }
+
+    /**
+     * @return True iff swapping is in progress. This is true till the content view is completely
+     *         swapped in.
+     */
+    public boolean isPageSwappingInProgress() {
+        return mSwapInProgress;
+    }
+
+    /**
+     * @return The {@link ContentViewCore} associated with the current background page.
+     */
+    public ContentViewCore getContentViewCore() {
+        return mContentViewCore;
+    }
+
+    /** @return The recent progress of background content view. */
+    public int getProgress() {
+        return mLoadProgress;
+    }
+
+    /**
+     * Loads the specified URL in the background content view.
+     * @param url the url to load.
+     */
+    private void loadUrl(String url) {
+        if (mNativeBackgroundContentViewHelperPtr == 0) return;
+
+        if (mContentViewCore == null) return;
+
+        mContentViewCore.onShow();
+
+        LoadUrlParams loadUrlParams = new LoadUrlParams(url);
+        // Use the referrer of preview url as referrer for original url.
+        // We are always loading url during onDidStartProvisionalLoadForFrame of preview URL, where
+        // load is not yet committed and so is the navigation entry. The current active
+        // navigation entry is still the referrer for preview url.
+        String referrerString = mTab.getWebContents()
+                .getNavigationController().getOriginalUrlForVisibleNavigationEntry();
+        Uri referrer = getUri(referrerString);
+        String referrerHost = referrer.getHost();
+        if (referrerHost == null
+                || TextUtils.indexOf(referrerHost, GOOGLE_DOMAIN_PREFIX) != 0) {
+            referrerHost = "www.google.com";
+        }
+        // We come here only through google.com and google.com always sends the referrer with
+        // value at least equal to the origin (and full url in http requests).
+        // Add 'gcjeid' param to referrer so that the PLT metrics are logged in a different bucket.
+        // PLT metrics are logged in a  different bucket if the referer contains 'gcjeid' param.
+        // For Experiment: gcjeid=19
+        String referrerTrimmed = "http://" + referrerHost + "/?"
+                + GWS_CHROME_JOINT_EXPERIMENT_ID_STRING + "=19";
+        loadUrlParams.setReferrer(new Referrer(referrerTrimmed, 0 /* WebReferrerPolicyAlways */));
+        mContentViewCore.getWebContents().getNavigationController().loadUrl(loadUrlParams);
+    }
+
+    /**
+     * Releases the ownership of the content view created. Also, resets the whole state of the
+     * current object.
+     */
+    private ContentViewCore releaseContentViewCore() {
+        mTab.detachOverlayContentViewCore(mContentViewCore);
+
+        ContentViewCore originalContentViewCore = mContentViewCore;
+        if (mContentViewCore != null && mNativeBackgroundContentViewHelperPtr != 0) {
+            nativeReleaseWebContents(mNativeBackgroundContentViewHelperPtr);
+        }
+        reset();
+        return originalContentViewCore;
+    }
+
+    /**
+     * Destroys the contentview and the corresponding native object.
+     */
+    private void destroy() {
+        if (mCurrentViewWebContentsObserver != null) {
+            mCurrentViewWebContentsObserver.destroy();
+            mCurrentViewWebContentsObserver = null;
+        }
+        destroyContentViewCore();
+
+        if (mNativeBackgroundContentViewHelperPtr == 0) return;
+
+        nativeDestroy(mNativeBackgroundContentViewHelperPtr);
+        mNativeBackgroundContentViewHelperPtr = 0;
+    }
+
+    /**
+     * Creates a new {@link ContentViewCore} and loads the given url.
+     * @param url Url to load.
+     */
+    private void createContentViewCoreWithUrl(String url) {
+        if (url == null || mNativeBackgroundContentViewHelperPtr == 0) return;
+
+        destroyContentViewCore();
+
+        Activity activity = mWindowAndroid.getActivity().get();
+        mContentViewCore = new ContentViewCore(activity);
+        ContentView cv = new ContentView(activity, mContentViewCore);
+        mContentViewCore.initialize(cv, cv,
+                ContentViewUtil.createWebContents(mTab.isIncognito(), false), mWindowAndroid);
+
+        // The renderer should be set with the height considering the top controls(non-fullscreen
+        // mode).
+        mContentViewCore.setTopControlsHeight(mContentViewCore.getTopControlsHeightPix(), true);
+        mWebContentsObserver = new WebContentsObserver(mContentViewCore.getWebContents()) {
+            @Override
+            public void didFirstVisuallyNonEmptyPaint() {
+                mPaintedNonEmpty = true;
+                trySwappingBackgroundView();
+            }
+            @Override
+            public void didStartProvisionalLoadForFrame(long frameId, long parentFrameId,
+                    boolean isMainFrame, String validatedUrl, boolean isErrorPage,
+                    boolean isIframeSrcdoc) {
+                if (isMainFrame) mDidStartLoad = true;
+            }
+
+            @Override
+            public void didFinishLoad(long frameId, String validatedUrl, boolean isMainFrame) {
+                if (isMainFrame) {
+                    mDidFinishLoad = true;
+                    trySwappingBackgroundView();
+                }
+            }
+
+            @Override
+            public void didFailLoad(boolean isProvisionalLoad,
+                    boolean isMainFrame, int errorCode, String description, String failingUrl) {
+                if (isMainFrame) {
+                    RecordHistogram.recordEnumeratedHistogram(
+                            "InstantSearchClicks.ReasonForSwap",
+                            SWAP_REASON_ORIGINAL_FAIL, SWAP_REASON_BOUNDARY);
+                    mDidFinishLoad = true;
+                    trySwappingBackgroundView();
+                }
+            }
+        };
+
+        mContentViewCore.setContentViewClient(new ContentViewClient() {
+            @Override
+            public void onOffsetsForFullscreenChanged(
+                    float topControlsOffsetYPix,
+                    float contentOffsetYPix,
+                    float overdrawBottomHeightPix) {
+                // Using onOffsetsForFullscreenChanged, as it is called on every frame update.
+                // Here we know that we have an update to frame. Ideally we need a function like
+                // onUpdateFrame.
+                if (mPaintedNonEmpty
+                        // We need to make sure the frame we got has some content. Sometimes
+                        // didFirstVisuallyNonEmptyPaint is called, but still the frame is empty and
+                        // has the default width of Chrome '980'px. So waiting for the contentWidth
+                        // of both preview and original to become same. Ideally in all cases they
+                        // should be same as they both are same content. Also if we get hung here
+                        // for some pages in the worst cases we swap on full load of original, or
+                        // our hard timeout will kick in.
+                        && getContentViewCore().getContentWidthCss()
+                                == mTab.getContentViewCore().getContentWidthCss()
+                        && !mSwapInProgress) {
+                    mNumRendererFramesReceived++;
+                    trySwappingBackgroundView();
+                }
+            }
+        });
+
+        if (mSwapTimeoutMs > 0) mHandler.postDelayed(mSwapOnTimeout, mSwapTimeoutMs);
+
+        nativeSetWebContents(mNativeBackgroundContentViewHelperPtr,
+                mContentViewCore, mWebContentsDelegate);
+
+        mBackgroundLoadStartTimeStampMs = System.currentTimeMillis();
+
+        loadUrl(url);
+        // Keep the toolbar always show in background view.
+        mContentViewCore.getWebContents().updateTopControlsState(false, true, false);
+        mTab.attachOverlayContentViewCore(mContentViewCore, false);
+    }
+
+    /**
+     * Helper to delete {@link ContentViewCore} and it's native web contents object.
+     */
+    private void destroyContentViewCore() {
+        if (mContentViewCore != null && mNativeBackgroundContentViewHelperPtr != 0) {
+            RecordHistogram.recordTimesHistogram(
+                    "InstantSearchClicks.TimeInPreview",
+                    System.currentTimeMillis() - mBackgroundLoadStartTimeStampMs,
+                    TimeUnit.MILLISECONDS);
+            mTab.detachOverlayContentViewCore(mContentViewCore);
+            mContentViewCore.destroy();
+            nativeDestroyWebContents(mNativeBackgroundContentViewHelperPtr);
+        }
+        reset();
+        // Note: We cannot set these in reset(), as we call reset() from releaseContentView and
+        // these values are used after that.
+        mSwapInProgress = false;
+        mLoadProgress = 0;
+        mDidStartLoad = false;
+        mDidFinishLoad = false;
+    }
+
+    /**
+     * @return True iff Background view has finished loading or all the following conditions are
+     *         met.
+     *         1. Preview page has loaded completely.
+     *         2. Background view has loaded atleast of preview page height.
+     *         3. Background view has painted anything non-empty.
+     */
+    private boolean isBackgroundViewReady() {
+        if (mDidFinishLoad) return true;
+
+        if (!mPreviewLoaded) return false;
+
+        if (!mPaintedNonEmpty) return false;
+
+        if (mNumRendererFramesReceived < mMinRendererFramesNeededForSwap) return false;
+
+        if (!hasBackgroundPageLoadedMoreThanPreview()) return false;
+
+        return true;
+    }
+
+    /** Called when any of the conditions needed for background view swap are met. */
+    private void trySwappingBackgroundView() {
+        if (mSwapInProgress) return;
+        // This function is asynchronously called from various places.
+        // So make sure we have background content view before doing anything.
+        if (!hasPendingBackgroundPage()) return;
+        if (isBackgroundViewReady()) backgroundViewReady();
+    }
+
+    /** Called when we are ready to swap in background view to foreground. */
+    private void backgroundViewReady() {
+        if (mDelegate == null) return;
+        mSwapInProgress = true;
+        swapInBackgroundViewAfterScroll();
+    }
+
+    private boolean isGooglePreviewServerHost(String host) {
+        if (host == null) return false;
+        return TextUtils.equals(host, GOOGLE_PREVIEW_SERVER_PREFIX + GOOGLE_PREVIEW_SERVER_SUFFIX)
+                || (ChromeVersionInfo.isDevBuild() && host.endsWith(GOOGLE_PREVIEW_SERVER_SUFFIX)
+                && host.contains("promise"));
+    }
+
+    private Uri getUri(String url) {
+        return Uri.parse(url == null ? "" : url);
+    }
+
+    /**
+     * @return original url if the passed in url is a preview url, else null.
+     */
+    private String getOriginalUrlForPreviewUrl(String previewUrl) {
+        Uri previewUri = getUri(previewUrl);
+        String originalUrl = null;
+        if (isGooglePreviewServerHost(previewUri.getHost())) {
+            try {
+                originalUrl = (new URL(previewUri.getQueryParameter("url"))).toString();
+            } catch (MalformedURLException mue) {
+                originalUrl = null;
+            }
+        }
+        return originalUrl;
+    }
+
+
+    /**
+     * Checks if the incoming url is instant search clicks eligible url. Only urls with referer
+     * containing google search domain and 'gcjeid' param are instant search clicks eligible url.
+     * @param url Url string.
+     */
+    private boolean isInstantSearchClicksControlUrl(String url) {
+        String referrer = mTab.getContentViewCore().getWebContents()
+                .getNavigationController().getOriginalUrlForVisibleNavigationEntry();
+        Uri referrerUri = getUri(referrer);
+        Uri previewUri = getUri(url);
+        if (referrerUri.getHost() == null || previewUri.getHost() == null) return false;
+        // Check if the url is coming from search page and has gcjeid param.
+        // TODO(ksimbili): Make this check stricter.
+        return (TextUtils.indexOf(referrerUri.getHost(), GOOGLE_DOMAIN_PREFIX) == 0
+                && referrerUri.getQueryParameter(GWS_CHROME_JOINT_EXPERIMENT_ID_STRING) != null
+                && TextUtils.indexOf(previewUri.getHost(), GOOGLE_DOMAIN_PREFIX) == -1);
+    }
+
+    private void setLogUma() {
+        // We ideally need to listen for gestures on current tab only while swapping to detect when
+        // scrolling ends(if one is active). But for UMA logging, we are listening for it always.
+        mTab.getContentViewCore().addGestureStateListener(mCurrentViewGestureStateListener);
+        mRecordUma = true;
+    }
+
+    private void resetLogUma() {
+        if (mTab.getContentViewCore() != null) {
+            mTab.getContentViewCore().removeGestureStateListener(mCurrentViewGestureStateListener);
+        }
+        mRecordUma = false;
+    }
+
+    /**
+     * Loads the original url in the background view, if the passed in url is a preview url.
+     * @param previewUrl Preview url string.
+     */
+    public void loadOriginalUrlIfPreview(String previewUrl) {
+        if (mExperimentGroup == INSTANT_SEARCH_CLICKS_EXPERIMENT_DISABLED) {
+            // If feature is disabled return;
+            return;
+        }
+
+        if (mExperimentGroup == INSTANT_SEARCH_CLICKS_EXPERIMENT_CONTROL
+                && isInstantSearchClicksControlUrl(previewUrl)) {
+            setLogUma();
+            return;
+        }
+
+        String originalUrl = getOriginalUrlForPreviewUrl(previewUrl);
+        if (originalUrl == null) return;
+
+        if (hasPendingBackgroundPage()) {
+            // The following condition is safe, as browser reload will always be on original url.
+            // Hence we will never encounter a situation where user is clicking on 'Reload' button
+            // and the page is not reloading.
+            if (originalUrl.equals(mContentViewCore.getWebContents().getUrl())) return;
+
+            // Log uma for the previous preview getting aborted
+            RecordHistogram.recordEnumeratedHistogram(
+                    "InstantSearchClicks.ReasonForSwap",
+                    SWAP_REASON_ABORT_ON_NAVIGATE, SWAP_REASON_BOUNDARY);
+        }
+
+        // Build content view.
+        createContentViewCoreWithUrl(originalUrl);
+
+        setLogUma();
+    }
+
+    /**
+     * Transfers zoom level from current cvc to the background cvc.
+     * @return Whether zoom level of background cvc had to be changed. It happens only when it is
+     *    different from current cvc.
+     */
+    private boolean transferPageScaleFactor() {
+        float currentViewPageScaleFactor =
+                mTab.getContentViewCore().getRenderCoordinates().getPageScaleFactor();
+
+        ContentViewCore backgroundViewCore = getContentViewCore();
+        RenderCoordinates rc = backgroundViewCore.getRenderCoordinates();
+
+        // Clamp the input value.
+        float newPageScaleFactor = Math.max(rc.getMinPageScaleFactor(),
+                Math.min(currentViewPageScaleFactor, rc.getMaxPageScaleFactor()));
+        if (newPageScaleFactor == rc.getPageScaleFactor()) return false;
+
+        float pageScaleFactorDelta = (newPageScaleFactor / rc.getPageScaleFactor());
+        backgroundViewCore.pinchByDelta(pageScaleFactorDelta);
+        mOriginalPageZoomed = true;
+        return true;
+    }
+
+    /**
+     * Transfers scroll offset from current cvc to the background cvc.
+     * @return Whether scroll offset of background cvc had to be changed. It happens only when it
+     *    is different from current cvc.
+     */
+    private boolean transferScrollOffset() {
+        ContentViewCore currentViewCore = mTab.getContentViewCore();
+        RenderCoordinates currentViewRenderCoordinates = currentViewCore.getRenderCoordinates();
+        float currentViewScrollX = currentViewRenderCoordinates.getScrollXPix();
+        float currentViewScrollY = currentViewRenderCoordinates.getScrollYPix();
+
+        ContentViewCore backgroundViewCore = getContentViewCore();
+        RenderCoordinates backgroundViewRenderCoordinates =
+                backgroundViewCore.getRenderCoordinates();
+        float maxHorizontalScroll = backgroundViewRenderCoordinates.getMaxHorizontalScrollPix();
+        float maxVerticalScroll = backgroundViewRenderCoordinates.getMaxVerticalScrollPix();
+
+        // Bound the scroll offsets to max scroll values.
+        float newScrollX = Math.min(currentViewScrollX, maxHorizontalScroll);
+        float newScrollY = Math.min(currentViewScrollY, maxVerticalScroll);
+
+        float backgroundViewScrollX = backgroundViewRenderCoordinates.getScrollXPix();
+        float backgroundViewScrollY = backgroundViewRenderCoordinates.getScrollYPix();
+        int scrollByX = Math.round(backgroundViewRenderCoordinates.fromPixToLocalCss(
+                newScrollX - backgroundViewScrollX));
+        int scrollByY = Math.round(backgroundViewRenderCoordinates.fromPixToLocalCss(
+                newScrollY - backgroundViewScrollY));
+
+        if (Math.abs(scrollByX) <= 1 && Math.abs(scrollByY) <= 1) return false;
+
+        if (!mOriginalPageZoomed) {
+            backgroundViewCore.scrollBy(Math.round(newScrollX - backgroundViewScrollX),
+                    Math.round(newScrollY - backgroundViewScrollY));
+        } else {
+            backgroundViewCore.scrollTo(Math.round(newScrollX), Math.round(newScrollY));
+        }
+        return true;
+    }
+
+    private void swapInBackgroundViewAfterScroll() {
+        getContentViewCore().addGestureStateListener(mBackgroundGestureStateListener);
+        syncPageStateAndSwapIfReady();
+    }
+
+    // Set scroll offset and zoom values from current cvc and swap the cvc if the both are synced.
+    private void syncPageStateAndSwapIfReady() {
+        // This function is asynchronously called from various places.
+        // So make sure we have background content view before doing anything.
+        if (!hasPendingBackgroundPage() || !isPageSwappingInProgress()) return;
+
+        ContentViewCore currentViewCore = mTab.getContentViewCore();
+        if (currentViewCore == null || currentViewCore.isScrollInProgress()) {
+            // We'll comeback here on scrollEnded and flingEndGesture.
+            return;
+        }
+
+        if (transferPageScaleFactor()) return;
+
+        if (transferScrollOffset()) return;
+
+        RenderCoordinates currentViewRenderCoordinates = currentViewCore.getRenderCoordinates();
+        int currentViewScrollY = currentViewRenderCoordinates.getScrollYPixInt();
+
+        int state;
+        if (currentViewScrollY == 0) {
+            state = PREVIEW_SCROLL_STATE_NO_SCROLL;
+        } else if (currentViewScrollY >= currentViewRenderCoordinates.getMaxVerticalScrollPix()) {
+            state = PREVIEW_SCROLL_STATE_SCROLL_AT_BOTTOM;
+        } else {
+            state = PREVIEW_SCROLL_STATE_SCROLL;
+        }
+        RecordHistogram.recordEnumeratedHistogram(
+                "InstantSearchClicks.PreviewScrollState", state, PREVIEW_SCROLL_STATE_BOUNDARY);
+        RecordHistogram.recordEnumeratedHistogram(
+                "InstantSearchClicks.ReasonForSwap", SWAP_REASON_REGULAR, SWAP_REASON_BOUNDARY);
+
+        // We are ready swap the view now.
+        swapInBackgroundView();
+    }
+
+    private void swapInBackgroundView() {
+        // This function is asynchronously called from various places.
+        // So make sure we have background content view before doing anything.
+        if (!hasPendingBackgroundPage()) return;
+
+        if (mTab.getContentViewCore() != null) {
+            mTab.getContentViewCore().removeGestureStateListener(mCurrentViewGestureStateListener);
+        }
+        getContentViewCore().removeGestureStateListener(mBackgroundGestureStateListener);
+        assert mDelegate != null;
+
+        // Make sure the ContentViewCore is visible.
+        getContentViewCore().setDrawsContent(true);
+
+        // Merge history stack before swap.
+        nativeMergeHistoryFrom(mNativeBackgroundContentViewHelperPtr, mTab.getWebContents());
+        ContentViewCore cvc = releaseContentViewCore();
+        mDelegate.onBackgroundViewReady(cvc, mDidStartLoad, mDidFinishLoad, mLoadProgress);
+
+        RecordHistogram.recordTimesHistogram("InstantSearchClicks.TimeToSwap",
+                System.currentTimeMillis() - mBackgroundLoadStartTimeStampMs,
+                TimeUnit.MILLISECONDS);
+
+        // Content view is released already, but still calling this to clear some state.
+        destroyContentViewCore();
+
+        // We need to include metrics from orignal page after swap too. For example, single tap
+        // metric should include taps in both preview and original page after swap. This we reset
+        // when tab commits a new navigation.
+        setLogUma();
+    }
+
+    /** Stop the current navigation. */
+    public void stopLoading() {
+        destroyContentViewCore();
+    }
+
+    /**
+     * Forces swapping of content views.
+     */
+    public void forceSwappingContentViews() {
+        RecordHistogram.recordEnumeratedHistogram(
+                "InstantSearchClicks.ReasonForSwap", SWAP_REASON_FORCE, SWAP_REASON_BOUNDARY);
+        swapInBackgroundView();
+    }
+
+    /**
+     * Calls 'unload' handler and deletes the webContents.
+     * @param webContents The webcontents to be deleted.
+     */
+    public void unloadAndDeleteWebContents(WebContents webContents) {
+        nativeUnloadAndDeleteWebContents(mNativeBackgroundContentViewHelperPtr, webContents);
+    }
+
+    /**
+     * Helper to reset the state of the object.
+     */
+    private void reset() {
+        mContentViewCore = null;
+        if (mWebContentsObserver != null) {
+            mWebContentsObserver.destroy();
+            mWebContentsObserver = null;
+        }
+
+        mPreviewLoaded = false;
+        mPaintedNonEmpty = false;
+        mNumRendererFramesReceived = 0;
+        resetLogUma();
+        mHandler.removeCallbacks(mSwapOnTimeout);
+        mOriginalPageZoomed = false;
+    }
+
+    @Override
+    public void onLoadProgressChanged(Tab tab, int progress) {
+        if (!hasPendingBackgroundPage()) return;
+        if (progress >= 100) {
+            mPreviewLoaded = true;
+            trySwappingBackgroundView();
+        }
+    }
+
+    @Override
+    public void onContentChanged(Tab tab) {
+        if (mCurrentViewWebContentsObserver != null) {
+            mCurrentViewWebContentsObserver.destroy();
+        }
+        if (tab.getContentViewCore() == null) return;
+
+        loadOriginalUrlIfPreview(mTab.getUrl());
+
+        mCurrentViewWebContentsObserver = new WebContentsObserver(mTab.getWebContents()) {
+            @Override
+            public void didFailLoad(boolean isProvisionalLoad,
+                    boolean isMainFrame, int errorCode, String description, String failingUrl) {
+                if (isMainFrame && hasPendingBackgroundPage()) {
+                    if (TextUtils.equals(mContentViewCore.getWebContents().getUrl(),
+                            getOriginalUrlForPreviewUrl(failingUrl))) {
+                        forceSwappingContentViews();
+                        RecordHistogram.recordEnumeratedHistogram(
+                                "InstantSearchClicks.ReasonForSwap",
+                                SWAP_REASON_ON_PREVIEW_FAIL, SWAP_REASON_BOUNDARY);
+                    }
+                }
+            }
+
+            @Override
+            public void didStartProvisionalLoadForFrame(long frameId, long parentFrameId,
+                    boolean isMainFrame, String validatedUrl, boolean isErrorPage,
+                    boolean isIframeSrcdoc) {
+                if (isMainFrame) {
+                    if (mTab.getContentViewCore() != null) {
+                        loadOriginalUrlIfPreview(validatedUrl);
+                    } else {
+                        destroyContentViewCore();
+                    }
+                }
+            }
+
+            @Override
+            public void didCommitProvisionalLoadForFrame(
+                    long frameId, boolean isMainFrame, String url, int transitionType) {
+                if (!isMainFrame) return;
+
+                if (!hasPendingBackgroundPage() && !isInstantSearchClicksControlUrl(url)) {
+                    resetLogUma();
+                }
+
+                if (hasPendingBackgroundPage() && getOriginalUrlForPreviewUrl(url) == null) {
+                    // We don't destroy the contentView in onDidStartProvisionalLoadForFrame, if the
+                    // url is navigating to non-preview URL. We instead do that here. Some urls
+                    // which are handled using intents, the url is never commited. In which case we
+                    // still want to swap to happen.
+                    destroyContentViewCore();
+                }
+            }
+        };
+    }
+
+    @Override
+    public void onDestroyed(Tab tab) {
+        destroy();
+    }
+
+    @CalledByNative
+    private long getNativePtr() {
+        return mNativeBackgroundContentViewHelperPtr;
+    }
+
+    public void recordBack() {
+        if (mRecordUma) RecordUserAction.record("MobilePreviewPageBack");
+    }
+
+    public void recordReload() {
+        if (mRecordUma) RecordUserAction.record("MobilePreviewPageReload");
+    }
+
+    public void recordTabClose() {
+        if (mRecordUma) RecordUserAction.record("MobilePreviewPageTabClose");
+    }
+
+    public void recordSingleTap() {
+        if (mRecordUma) RecordUserAction.record("MobilePreviewPageSingleTap");
+    }
+
+    private native long nativeInit();
+    private native void nativeDestroy(long nativeBackgroundContentViewHelper);
+    private native void nativeSetWebContents(long nativeBackgroundContentViewHelper,
+            ContentViewCore contentViewCore, WebContentsDelegateAndroid delegate);
+    private native void nativeDestroyWebContents(long nativeBackgroundContentViewHelper);
+    private native void nativeReleaseWebContents(long nativeBackgroundContentViewHelper);
+    private native void nativeMergeHistoryFrom(long nativeBackgroundContentViewHelper,
+            WebContents webContents);
+    private native void nativeUnloadAndDeleteWebContents(long nativeBackgroundContentViewHelper,
+            WebContents webContents);
+    private native int nativeGetSwapTimeoutMs(long nativeBackgroundContentViewHelper);
+    private native int nativeGetNumFramesNeededForSwap(long nativeBackgroundContentViewHelper);
+}