cc: Make the PictureLayerImpl raster source null until commit.

No need to make a raster source that is never used.

R=enne, vmpstr
BUG=387116

Review URL: https://codereview.chromium.org/809433003

Cr-Commit-Position: refs/heads/master@{#308466}
void CompareDrawQuad(DrawQuad* quad,
                     DrawQuad* copy,
                     SharedQuadState* copy_shared_state) {
  EXPECT_EQ(quad->material, copy->material);
  EXPECT_EQ(quad->rect, copy->rect);
  EXPECT_EQ(quad->visible_rect, copy->visible_rect);
  EXPECT_EQ(quad->opaque_rect, copy->opaque_rect);
  EXPECT_EQ(quad->needs_blending, copy->needs_blending);
  EXPECT_EQ(copy_shared_state, copy->shared_quad_state);
}

void CompareDrawQuad(DrawQuad* quad,
                     DrawQuad* copy,
                     SharedQuadState* copy_shared_state) {
  EXPECT_EQ(quad->material, copy->material);
  EXPECT_EQ(quad->rect, copy->rect);
  EXPECT_EQ(quad->visible_rect, copy->visible_rect);
  EXPECT_EQ(quad->opaque_rect, copy->opaque_rect);
  EXPECT_EQ(quad->needs_blending, copy->needs_blending);
  EXPECT_EQ(copy_shared_state, copy->shared_quad_state);
}
