Copy shaders from WR repo.

resources/shaders/ps_clear.vs.glsl

@@ -0,0 +1,23 @@
+#line 1
+
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+struct ClearTile {
+    uvec4 rect;
+};
+
+layout(std140) uniform Tiles {
+    ClearTile tiles[WR_MAX_CLEAR_TILES];
+};
+
+
+void main() {
+    ClearTile tile = tiles[gl_InstanceID];
+
+    vec4 rect = vec4(tile.rect);
+
+    vec4 pos = vec4(mix(rect.xy, rect.xy + rect.zw, aPosition.xy), 0, 1);
+    gl_Position = uTransform * pos;
+}