Remove -webkit-center from mediaControls.css for immersive-mode.

"text-align: -webkit-center" is a non-standard css property/value pair
which has undefined behaviour.

This was being used for centering the video controls within the video
player when in the "immersive-mode".

https://chromium-review.googlesource.com/c/chromium/src/+/1977196
...changed how the blink's layout codebase handles margins, removing a
bug for when "-webkit-center" is set on a child.

This patch changes the immersive-mode stylesheet to use:
"align-items: center" for centering the controls in their container.

It was also necessary to specify the width of the "timeline" to ensure
it filled the available space.

This also re-enables the disabled test.

Bug: 1041904
Change-Id: I6ca530a14185fa0bba8900824cef3b369728e90c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144777Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759418}

chrome/android/javatests/src/org/chromium/chrome/browser/vr/VrBrowserWebInputEditingTest.java

@@ -24,7 +24,6 @@ import org.junit.runner.RunWith;
 
 import org.chromium.base.test.BundleTestRule;
 import org.chromium.base.test.util.CommandLineFlags;
-import org.chromium.base.test.util.DisabledTest;
 import org.chromium.base.test.util.Feature;
 import org.chromium.base.test.util.Restriction;
 import org.chromium.chrome.browser.flags.ChromeSwitches;
@@ -438,7 +437,6 @@ public class VrBrowserWebInputEditingTest {
     @Test
     @MediumTest
     @Feature({"Browser", "RenderTest"})
-    @DisabledTest(message = "https://crbug.com/1041904")
     public void testFullscreenVideoControls()
             throws InterruptedException, TimeoutException, IOException {
         // There's occasionally slight AA differences along the play button, so tolerate a small

third_party/blink/renderer/modules/media_controls/resources/mediaControls.css

@@ -1349,6 +1349,7 @@ video::-webkit-media-controls.immersive-mode div[pseudo="-internal-media-control
 
 /* Timeline sizing does not include padding in max width. */
 video::-webkit-media-controls.immersive-mode input[pseudo="-webkit-media-controls-timeline" i] {
+  width: calc(100% - 64px);
   max-width: 471px;
   height: 5px;
   margin-bottom: 20px;
@@ -1363,7 +1364,7 @@ video::-webkit-media-controls.immersive-mode div[pseudo="-internal-media-control
 
 video::-webkit-media-controls.immersive-mode div[pseudo="-webkit-media-controls-panel" i] {
   /* Centering the button panel and timeline within the controls. */
-  text-align: -webkit-center;
+  align-items: center;
 
   /* Taller scrim. */
   background: