[whatwg] [canvas] Proposal for supportsContext

[Tobie Langel]

> This is actually what we could do now. We could hide window.WebGLRenderingContext
> when we can't create one. But then we'd have to hide all these too:
>
>        attribute [Conditional=WEBGL] WebGLActiveInfoConstructor WebGLActiveInfo;
>        attribute [Conditional=WEBGL] WebGLBufferConstructor WebGLBuffer;
>        attribute [Conditional=WEBGL] WebGLFramebufferConstructor WebGLFramebuffer;
>        attribute [Conditional=WEBGL] WebGLProgramConstructor WebGLProgram;
>        attribute [Conditional=WEBGL] WebGLRenderbufferConstructor WebGLRenderbuffer;
>        attribute [Conditional=WEBGL] WebGLRenderingContextConstructor WebGLRenderingContext;
>        attribute [Conditional=WEBGL] WebGLShaderConstructor WebGLShader;
>        attribute [Conditional=WEBGL] WebGLShaderPrecisionFormatConstructor WebGLShaderPrecisionFormat;
>        attribute [Conditional=WEBGL] WebGLTextureConstructor WebGLTexture;
>        attribute [Conditional=WEBGL] WebGLUniformLocationConstructor WebGLUniformLocation;

Oh my.  All of these are globals!? *Sigh*

--tobie