Allow binding multiple textures to one DC Layer overlay.

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 fab57426fb98c39da79396374d75e30c1227f2b6..7d9ee787f3be683cca1d67589e10e8b9952040f0 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -3232,14 +3232,14 @@ void GLRenderer::ScheduleDCLayers() {
        current_frame()->dc_layer_overlay_list) {
     DCHECK(!dc_layer_overlay.rpdq);
 
-    unsigned texture_id = 0;
+    int i = 0;
     for (const auto& contents_resource_id : dc_layer_overlay.resources) {
       if (contents_resource_id) {
         pending_overlay_resources_.push_back(
             base::MakeUnique<ResourceProvider::ScopedReadLockGL>(
                 resource_provider_, contents_resource_id));
-        if (!texture_id)
-          texture_id = pending_overlay_resources_.back()->texture_id();
+        gl_->SetDCLayerTextureCHROMIUM(
+            i++, pending_overlay_resources_.back()->texture_id());
       }
     }
     GLfloat contents_rect[4] = {
@@ -3269,7 +3269,7 @@ void GLRenderer::ScheduleDCLayers() {
           z_order, transform);
     }
     gl_->ScheduleDCLayerCHROMIUM(
-        texture_id, contents_rect, dc_layer_overlay.background_color,
+        contents_rect, dc_layer_overlay.background_color,

[ccameron, 2017/05/03 16:16:32]

It may just be easier to have ScheduleDCLayerCHROMIUM take an arrays of
texture_ids, something like

ScheduleDCLayerCHROMIUM(GLuint numTextures, GLuint* textures)

         dc_layer_overlay.edge_aa_mask, bounds_rect, filter);
   }