Implement autoplay gesture override experiment.

Source/core/html/AutoplayExperimentHelper.cpp

Index: Source/core/html/AutoplayExperimentHelper.cpp
diff --git a/Source/core/html/AutoplayExperimentHelper.cpp b/Source/core/html/AutoplayExperimentHelper.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..643eaceb0bda153f928cddc09d7c0cb8cba3cb46
--- /dev/null
+++ b/Source/core/html/AutoplayExperimentHelper.cpp
@@ -0,0 +1,180 @@
+// 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 "config.h"
+#include "core/html/AutoplayExperimentHelper.h"
+
+#include "core/dom/Document.h"
+#include "core/frame/Settings.h"
+#include "core/html/HTMLMediaElement.h"
+#include "core/layout/LayoutBox.h"
+#include "core/layout/LayoutObject.h"
+#include "core/layout/LayoutVideo.h"
+#include "core/layout/LayoutView.h"
+#include "core/page/Page.h"
+#include "platform/Logging.h"
+#include "platform/UserGestureIndicator.h"
+#include "platform/geometry/IntRect.h"
+
+namespace blink {
+
+using namespace HTMLNames;
+
+AutoplayExperimentHelper::AutoplayExperimentHelper(HTMLMediaElement& element)
+    : m_element(element)
+    , m_mode(AutoplayExperimentConfig::Mode::Off)
+    , m_playPending(false)
+{
+    if (document().settings()) {
+        m_mode = AutoplayExperimentConfig::fromString(document().settings()->autoplayExperimentMode());
+
+        if (m_mode != AutoplayExperimentConfig::Mode::Off) {
+            WTF_LOG(Media, "HTMLMediaElement: autoplay experiment set to %d",
+                m_mode);
+        }
+    }
+}
+
+AutoplayExperimentHelper::~AutoplayExperimentHelper()
+{
+}
+
+void AutoplayExperimentHelper::becameReadyToPlay()
+{
+    // Assuming that we're eligible to override the user gesture requirement,
+    // then play.
+    if (isEligible()) {
+        prepareToPlay(GesturelessPlaybackStartedByAutoplayFlagImmediately);
+    }
+}
+
+void AutoplayExperimentHelper::playMethodCalled()
+{
+    // Set the pending state, even if the play isn't going to be pending.
+    // Eligibility can change if, for example, the mute status changes.
+    // Having this set is okay.
+    m_playPending = true;
+
+    if (!UserGestureIndicator::processingUserGesture()) {
+
+        if (isEligible()) {
+            // Remember that userGestureRequiredForPlay is required for
+            // us to be eligible for the experiment.
+            // We are able to override the gesture requirement now, so
+            // do so.
+            prepareToPlay(GesturelessPlaybackStartedByPlayMethodImmediately);
+        }
+
+    }
+}
+
+void AutoplayExperimentHelper::pauseMethodCalled()
+{
+    // Don't try to autoplay, if we would have.
+    m_playPending = false;
+}
+
+void AutoplayExperimentHelper::mutedChanged()
+{
+    // In other words, start playing if we just needed 'mute' to autoplay.
+    maybeStartPlaying();
+}
+
+bool AutoplayExperimentHelper::maybeStartPlaying()
+{
+    // See if we're allowed to autoplay now.
+    if (!isEligible()) {
+        return false;
+    }
+
+    // Start playing!
+    prepareToPlay(m_element.shouldAutoplay()
+        ? GesturelessPlaybackStartedByAutoplayFlagAfterScroll
+        : GesturelessPlaybackStartedByPlayMethodAfterScroll);
+    m_element.playInternal();
+
+    return true;
+}
+
+bool AutoplayExperimentHelper::isEligible() const
+{
+    // If no user gesture is required, then the experiment doesn't apply.
+    // This is what prevents us from starting playback more than once.
+    // Since this flag is never set to true once it's cleared, it will block
+    // the autoplay experiment forever.
+    if (!m_element.isUserGestureRequiredForPlay())
+        return false;
+
+    if (m_mode == AutoplayExperimentConfig::Mode::Off)
+        return false;
+
+    // Make sure that this is an element of the right type.
+    if (!enabled(AutoplayExperimentConfig::Mode::ForVideo)
+        && isHTMLVideoElement(m_element))
+        return false;
+
+    if (!enabled(AutoplayExperimentConfig::Mode::ForAudio)
+        && isHTMLAudioElement(m_element))
+        return false;
+
+    // If nobody has requested playback, either by the autoplay attribute or
+    // a play() call, then do nothing.
+    if (!m_playPending && !m_element.shouldAutoplay())
+        return false;
+
+    // If the video is already playing, then do nothing.  Note that there
+    // is not a path where a user gesture is required but the video is
+    // playing.  However, we check for completeness.
+    if (!m_element.paused())
+        return false;
+
+    // Note that the viewport test always returns false on desktop, which is
+    // why video-autoplay-experiment.html doesn't check -ifmobile .
+    if (enabled(AutoplayExperimentConfig::Mode::IfMobile)
+        && !document().viewportDescription().isLegacyViewportType())
+        return false;
+
+    // If media is muted, then autoplay when it comes into view.

[philipj_slow, 2015/09/04 09:24:27]

This "when it comes into view" and other comments like it (below) should be
moved to the following CL I think.

[liberato (no reviews please), 2015/09/08 21:58:01]

done, and also this does the wrong thing.  checking for mutedAttr will succeed
even if it were unmuted by JS.

[philipj_slow, 2015/09/10 10:05:13]

I can't see the change for this in PS28 either.

[liberato (no reviews please), 2015/09/10 14:52:27]

oh, bother.  i inadvertently switched to the branch with the visibility checks
when i made some of these changes.  sorry about that.

+    if (enabled(AutoplayExperimentConfig::Mode::IfMuted))
+        return m_element.fastHasAttribute(mutedAttr) || m_element.muted();
+
+    // Autoplay when it comes into view (if needed), maybe muted.
+    return true;
+}
+
+void AutoplayExperimentHelper::muteIfNeeded()
+{
+    if (enabled(AutoplayExperimentConfig::Mode::PlayMuted)) {
+        ASSERT(!isEligible());
+        // If we are actually changing the muted state, then this will call
+        // mutedChanged().  If isEligible(), then mutedChanged() will try
+        // to start playback, which we should not do here.
+        m_element.setMuted(true);
+    }
+}
+
+void AutoplayExperimentHelper::prepareToPlay(AutoplayMetrics metric)
+{
+    m_element.recordAutoplayMetric(metric);
+
+    // This also causes !isEligible, so that we don't allow autoplay more than
+    // once.  Be sure to do this before muteIfNeeded().
+    m_element.removeUserGestureRequirement();
+
+    muteIfNeeded();
+
+    // Record that this autoplayed without a user gesture.  This is normally
+    // set when we discover an autoplay attribute, but we include all cases
+    // where playback started without a user gesture, e.g., play().
+    m_element.setInitialPlayWithoutUserGestures(true);
+
+    // Do not actually start playback here.
+}
+
+Document& AutoplayExperimentHelper::document() const
+{
+    return m_element.document();
+}
+
+}