Remove force composition from animation worklet layout test

Previously we have to force compositing the animated target for worklet
animations. Given that the target with worklet animations has been
composited automatically after crrev.com/c/930128, there is no need to
keep the force composition in the test.

Change-Id: I5effd169844e0c08a3578b35ccacf886965fce37
Reviewed-on: https://chromium-review.googlesource.com/1167988Reviewed-by: Majid Valipour <majidvp@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584946}

third_party/WebKit/LayoutTests/virtual/threaded/fast/animationworklet/animation-worklet-inside-iframe.html

@@ -4,7 +4,6 @@
   width: 100px;
   height: 100px;
   background-color: #ff0000;
-  will-change: opacity;
 }
 </style>
 <script id="main_worklet" type="text/worklet">

third_party/WebKit/LayoutTests/virtual/threaded/fast/animationworklet/animator-animate.html

@@ -20,7 +20,7 @@ registerAnimator("test_animator", class {
 });
 </script>
 
-<div id="target" style="will-change: transform, opacity;"></div>
+<div id="target"></div>
 
 <script src="resources/animation-worklet-tests.js"></script>
 <script>

third_party/WebKit/LayoutTests/virtual/threaded/fast/animationworklet/animator-with-options.html

@@ -23,7 +23,7 @@ registerAnimator("test_animator", class {
 });
 </script>
 
-<div id="target" style="will-change: transform, opacity;"></div>
+<div id="target"></div>
 
 <script src="resources/animation-worklet-tests.js"></script>
 <script>

third_party/WebKit/LayoutTests/virtual/threaded/fast/animationworklet/resources/animator-iframe.html

@@ -4,7 +4,6 @@
   width: 100px;
   height: 100px;
   background-color: #00ff00;
-  will-change: opacity;
 }
 </style>
 <script src="animation-worklet-tests.js"></script>

third_party/WebKit/LayoutTests/virtual/threaded/fast/animationworklet/worklet-animation-cancel.html

@@ -4,7 +4,6 @@
   width: 100px;
   height: 100px;
   background-color: #0000ff;
-  will-change: transform;  /* force compositing */
 }
 </style>
 

third_party/WebKit/LayoutTests/virtual/threaded/fast/animationworklet/worklet-animation-style-update.html

@@ -4,11 +4,6 @@
   width: 100px;
   height: 100px;
   background-color: #00ff00;
-  /*
-  * Force compositing.
-  * TODO(majidvp): Should not be needed when http://crbug.com/776533 is fixed.
-  */
-  will-change: transform, opacity;
 }
 
 </style>