command_buffer: Make inactive bound fragment inputs reserve the location

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_path_rendering.txt

 Name
 
     CHROMIUM_path_rendering
 
 Name Strings
 
     GL_CHROMIUM_path_rendering
 
 Version
 
@@ skipping 1009 matching lines @@
     "gl_" prefix.
 
     When a program is linked, any active uniforms without a binding specified
     through BindFragmentInputLocation will be automatically be bound to
     locations by the GL. Such bindings can not be queried.
 
     BindFragmentInputLocation may be issued before any shader objects are
     attached to a program object. Hence it is allowed to bind any name (except
     a name starting with "gl_") to an index, including a name that is never used
     as a varying in the fragment shader object. Assigned bindings for varying
-    variables that do not exist or are not active are ignored.
+    variables that do not exist or are not active are ignored. Using such bindings
+    behaves as if passed location was -1.
 
     It is possible for an application to bind more than one fragment
     input name to the same location.  This is referred to as aliasing.
     This will only work if only one of the aliased fragment inputs is
     active in the executable program, or if no path through the shader
     consumes more than one fragment input of a set of fragment inputs
     aliased to the same location.  If two statically used fragment
     inputs in a program are bound to the name location, link must
     fail.
 
@@ skipping 353 matching lines @@
          * Paths wind by default counterclockwise
          * Window space transform can reverse this winding
          * GL front face state CW/CCW selects whether the variable is true
            or false
 
         user-defined varyings: constant zeros.
 
 Revision History
 
     14/8/2014    Documented the extension