Adds keyboard functionality for videos.

third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp

Index: third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp
diff --git a/third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp b/third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp
index b31c8faab967c0c281f1f35b1a003a6e333a1bea..e0745b19540eb5c56288b308373d0ab319ddef4f 100644
--- a/third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp
+++ b/third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp
@@ -33,6 +33,7 @@
 #include "core/dom/ResizeObserverCallback.h"
 #include "core/dom/ResizeObserverEntry.h"
 #include "core/dom/TaskRunnerHelper.h"
+#include "core/events/KeyboardEvent.h"
 #include "core/events/MouseEvent.h"
 #include "core/frame/Settings.h"
 #include "core/frame/UseCounter.h"
@@ -766,6 +767,23 @@ void MediaControlsImpl::DefaultEventHandler(Event* event) {
   if (event->type() == EventTypeNames::focusin ||
       event->type() == EventTypeNames::input)
     ResetHideMediaControlsTimer();
+
+  if (event->IsKeyboardEvent()) {

[mlamouri (slow - plz ping), 2017/05/09 17:32:10]

I realised the other day (not sure why I was thinking about this) that this
might conflict with websites keyboard event handling. Should we add a check like
`MediaElement().ShouldShowControls()`? And add a test checking that these
shortcuts do not apply if `controls` isn't set?

[lethalantidote, 2017/05/18 00:03:34]

Done.

+    const String& key = ToKeyboardEvent(event)->key();
+    if (key == "Enter" || ToKeyboardEvent(event)->keyCode() == ' ') {
+      play_button_->OnMediaKeyboardEvent(event);
+      return;
+    }
+    if (key == "ArrowLeft" || key == "ArrowRight" || key == "Home" ||
+        key == "End") {
+      timeline_->OnMediaKeyboardEvent(event);
+      return;
+    }
+    if (key == "ArrowDown" || key == "ArrowUp") {
+      volume_slider_->OnMediaKeyboardEvent(event);
+      return;
+    }
+  }
 }
 
 void MediaControlsImpl::HideMediaControlsTimerFired(TimerBase*) {