Add flag for enabling/disabling video fullscreen detection

third_party/WebKit/Source/core/html/HTMLVideoElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLVideoElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLVideoElement.cpp b/third_party/WebKit/Source/core/html/HTMLVideoElement.cpp
index f0c93fd8584c1bfad56cb8d4cb5ca9dc7dd233c4..90a86f6e9897604811faebcbd56eb3150fb0f959 100644
--- a/third_party/WebKit/Source/core/html/HTMLVideoElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLVideoElement.cpp
@@ -54,13 +54,16 @@ namespace blink {
 using namespace HTMLNames;
 
 inline HTMLVideoElement::HTMLVideoElement(Document& document)
-    : HTMLMediaElement(videoTag, document),
-      m_customControlsFullscreenDetector(
-          new MediaCustomControlsFullscreenDetector(*this)) {
+    : HTMLMediaElement(videoTag, document) {
   if (document.settings()) {
     m_defaultPosterURL =
         AtomicString(document.settings()->getDefaultVideoPosterURL());
   }
+
+  if (RuntimeEnabledFeatures::videoFullscreenDetectionEnabled()) {
+    m_customControlsFullscreenDetector =
+        new MediaCustomControlsFullscreenDetector(*this);
+  }
 }
 
 HTMLVideoElement* HTMLVideoElement::create(Document& document) {
@@ -77,7 +80,9 @@ DEFINE_TRACE(HTMLVideoElement) {
 }
 
 void HTMLVideoElement::contextDestroyed(ExecutionContext* context) {
-  m_customControlsFullscreenDetector->contextDestroyed();
+  if (m_customControlsFullscreenDetector)
+    m_customControlsFullscreenDetector->contextDestroyed();
+
   HTMLMediaElement::contextDestroyed(context);
 }