what is a persistent video?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5cd9ae8889c732428043460caa5d0fd8043041c1

commit 5cd9ae8889c732428043460caa5d0fd8043041c1
Author: mlamouri <mlamouri@chromium.org>
Date: Sat Feb 18 11:05:09 2017

Don't show media controls when there is a persistent video.

When a video becomes persistent, the WebContents is notified and will
then update the preferences so Blink doesn't show the native controls.

BUG= 691619 

Review-Url: https://codereview.chromium.org/2692903002
Cr-Commit-Position: refs/heads/master@{#451454}

[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/renderer_host/render_view_host_delegate.cc
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/renderer_host/render_view_host_delegate.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/renderer_host/render_view_host_impl.cc
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/web_contents/web_contents_android.cc
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/web_contents/web_contents_android.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/web_contents/web_contents_impl.cc
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/browser/web_contents/web_contents_impl.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/public/android/java/src/org/chromium/content/browser/webcontents/WebContentsImpl.java
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/public/android/java/src/org/chromium/content_public/browser/WebContents.java
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/public/common/common_param_traits_macros.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/public/common/web_preferences.cc
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/public/common/web_preferences.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/content/renderer/render_view_impl.cc
[add] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/LayoutTests/media/controls/settings-disable-controls.html
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/frame/Settings.json5
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/frame/SettingsDelegate.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/html/HTMLMediaElement.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/html/shadow/MediaControls.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/html/shadow/MediaControlsTest.cpp
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/core/page/Page.cpp
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/web/WebSettingsImpl.cpp
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/Source/web/WebSettingsImpl.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/third_party/WebKit/public/web/WebSettings.h
[modify] https://crrev.com/5cd9ae8889c732428043460caa5d0fd8043041c1/tools/metrics/histograms/histograms.xml