gpu: support GL_TEXTURE_CUBE_MAP destination target to Copy(Sub)TextureCHROMIUM.

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt

 Name
 
     CHROMIUM_copy_texture
 
 Name Strings
 
     GL_CHROMIUM_copy_texture
 
 Version
 
@@ skipping 64 matching lines @@
     If <unpack_premultiply_alpha> and <unpack_unmultiply_alpha> are true,
     no alpha processing occurs.  This is the equivalent of having neither flag
     set.
 
     INVALID_OPERATION is generated if <internal_format> is not one of the valid formats
     described above.
 
     INVALID_OPERATION is generated if the internal format of <source_id> is not one of
     formats from the table above.
 
-    INVALID_VALUE is generated if <target> is not GL_TEXTURE_2D.
+    INVALID_VALUE is generated if <target> is not GL_TEXTURE_2D,
+    GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X,
+    GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y,
+    GL_TEXTURE_CUBE_MAP_POSITIVE_Z, or GL_TEXTURE_CUBE_MAP_NEGATIVE_Z.
 
     INVALID_VALUE is generated if <source_id> or <dest_id> are not valid texture
     objects.
 
     INVALID_VALUE is generated if textures corresponding to <dest_id> have not
-    been bound as GL_TEXTURE_2D object.
+    been bound as GL_TEXTURE_2D or GL_TEXTURE_CUBE_MAP object.
+
+    INVALID_VALUE is generated if the bound target of textures corresponding to
+    <dest_id> doesn't match <target>.
 
     INVALID_VALUE is generated if textures corresponding to <source_id> have not
     been bound as GL_TEXTURE_2D, GL_TEXTURE_RECTANGLE_ARB or
     GL_TEXTURE_EXTERNAL_OES objects.
 
     INVALID_VALUE is generated if level 0 of the source texture is not defined.
 
     The command
 
         void glCopySubTextureCHROMIUM (GLenum target, GLenum source_id,
@@ skipping 17 matching lines @@
     <x> and <y> specify specify a texel offset in the x and y direction
     respectively within the source texture.
 
     <width> specifies the width of the texture subimage.
 
     <height> specifies the width of the texture subimage.
 
     INVALID_OPERATION is generated if source internal_format and destination
     internal_format are not one of the valid formats described above.
 
-    INVALID_VALUE is generated if <target> is not GL_TEXTURE_2D.
+    INVALID_VALUE is generated if <target> is not GL_TEXTURE_2D,
+    GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X,
+    GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y,
+    GL_TEXTURE_CUBE_MAP_POSITIVE_Z, or GL_TEXTURE_CUBE_MAP_NEGATIVE_Z.
 
     INVALID_OPERATION is generated if the destination texture has not been
     defined.
 
     INVALID_VALUE is generated if level 0 of the source texture or
     the destination texture is not defined.
 
     INVALID_VALUE is generated if <xoffset> < 0 , or <yoffset> < 0.
 
     INVALID_VALUE is generated if (<xoffset> + source_width) > dest_width,
@@ skipping 16 matching lines @@
 
     None.
 
 Revision History
 
     8/1/2011    Documented the extension
     7/4/2013    Add a new parameter dest_type to glCopyTextureCHROMIUM()
     16/7/2014   Add GL_TEXTURE_RECTANGLE_ARB as valid source_id target
     19/6/2015   Add arguments unpack_flip_y, unpack_premultiply_alpha, and
                 unpack_unmultiply_alpha to both commands.
+    6/8/2015    support GL_TEXTURE_CUBE_MAP destination target.