cc: Fix masks when the RenderPassDrawQuad does not cover the whole pass

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index 04c1158d3b10d01ec60e6824f94423447bf938c5..bf76071b4c3e82c1acd6320afb0bd75cca4f1b68 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -1011,9 +1011,10 @@ void GLRenderer::DrawRenderPassQuad(DrawingFrame* frame,
     // and the RenderPass contents texture, so we flip the tex coords from the
     // RenderPass texture to find the mask texture coords.
     GLC(Context(),
-        Context()->uniform2f(shader_mask_tex_coord_offset_location,
-                             quad->mask_uv_rect.x(),
-                             quad->mask_uv_rect.y() + mask_tex_scale_y));
+        Context()->uniform2f(
+            shader_mask_tex_coord_offset_location,
+            quad->mask_uv_rect.x(),
+            quad->mask_uv_rect.y() + quad->mask_uv_rect.height()));
     GLC(Context(),
         Context()->uniform2f(shader_mask_tex_coord_scale_location,
                              mask_tex_scale_x,