mediaplayer: trigger hardware acceleration closer to player

This is a workaround for a regression to fix the missing video in the MediaPlayer as reported in bug 15310. It is a followup to
http://codereview.chromium.org/6969027/

BUG=chromium-os:15310
TEST=ran manually to see the video
Review URL: http://codereview.chromium.org/7065017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@86539 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/file_manager/slideshow.html

@@ -8,7 +8,6 @@
 body {
   overflow: hidden;
   background: black;
-  -webkit-transform: translateZ(0);
 }
 
 #glow {
@@ -28,6 +27,7 @@ body {
   top: 0;
   bottom: 30px;
   overflow: hidden;
+  -webkit-transform: translateZ(0);
 }
 
 #playercontrols {

chrome/browser/resources/mediaplayer.html

@@ -8,7 +8,6 @@
 body {
   overflow: hidden;
   background: black;
-  -webkit-transform: translateZ(0);
 }
 
 .error {
@@ -222,6 +221,7 @@ body {
   position: absolute;
   left: 0;
   top: 0;
+  -webkit-transform: translateZ(0);
 }
 
 .duration {