Pass InterfaceBlockLinker to ProgramImpl::link.

This change is in preparation for moving the linking logic to the
Implementation.

Introduces a ProgramLinkedResources class that is passed into the Impl
and holds linking-related info such as the UBOs, Varyings, etc.

BUG=angleproject:2208

Change-Id: I2ef0824b54bfb462c79d003bffe34e9cfad60d8a
Reviewed-on: https://chromium-review.googlesource.com/746204
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/renderer/null/ProgramNULL.h b/src/libANGLE/renderer/null/ProgramNULL.h
index 5f8c464..61ff61b 100644
--- a/src/libANGLE/renderer/null/ProgramNULL.h
+++ b/src/libANGLE/renderer/null/ProgramNULL.h
@@ -29,7 +29,7 @@
     void setSeparable(bool separable) override;
 
     gl::LinkResult link(const gl::Context *context,
-                        const gl::VaryingPacking &packing,
+                        const gl::ProgramLinkedResources &resources,
                         gl::InfoLog &infoLog) override;
     GLboolean validate(const gl::Caps &caps, gl::InfoLog *infoLog) override;