Remove the unused data member in YuvImage.

The color_space condition will be replaced by the shader preprocessor.
The y_st_rect, u_st_rect and v_st_rect are not used in shader.

webrender/res/prim_shared.glsl

@@ -747,21 +747,13 @@ Image fetch_image(int index) {
     return Image(data);
 }
 
-// YUV color spaces
-#define YUV_REC601 1
-#define YUV_REC709 2
-
 struct YuvImage {
-    vec4 y_st_rect;
-    vec4 u_st_rect;
-    vec4 v_st_rect;
     vec2 size;
-    int color_space;
 };
 
 YuvImage fetch_yuv_image(int index) {
     vec4 data = fetch_data_1(index);
-    return YuvImage(vec4(0.0), vec4(0.0), vec4(0.0), data.xy, int(data.z));
+    return YuvImage(data.xy);
 }
 
 struct BoxShadow {

webrender/src/prim_store.rs

@@ -175,16 +175,14 @@ pub struct YuvImagePrimitiveCpu {
 #[repr(C)]
 pub struct YuvImagePrimitiveGpu {
     pub size: LayerSize,
-    pub color_space: f32,
-    pub padding: f32,
+    pub padding: [f32; 2],
 }
 
 impl YuvImagePrimitiveGpu {
-    pub fn new(size: LayerSize, color_space: YuvColorSpace) -> Self {
+    pub fn new(size: LayerSize) -> Self {
         YuvImagePrimitiveGpu {
             size: size,
-            color_space: color_space as u32 as f32,
-            padding: 0.0,
+            padding: [0.0; 2],
         }
     }
 }