Backed out changeset a510c6ccaeb2 (bug 1372438) for various webgl test failures a=backout

MozReview-Commit-ID: FnMPcPkbtFX

dom/webidl/WebGLRenderingContext.webidl

@@ -482,6 +482,7 @@ interface WebGLRenderingContextBase {
     const GLenum RGB5_A1                        = 0x8057;
     const GLenum RGB565                         = 0x8D62;
     const GLenum DEPTH_COMPONENT16              = 0x81A5;
+    const GLenum STENCIL_INDEX                  = 0x1901;
     const GLenum STENCIL_INDEX8                 = 0x8D48;
     const GLenum DEPTH_STENCIL                  = 0x84F9;