Revert 168457 "WebGL: Transfer ownership of WebGraphicsContext3D..."

Caused assertion failures on debug GPU bots. See Issue 344393 for details.

> WebGL: Transfer ownership of WebGraphicsContext3D from WebGLRenderingContext to DrawingBuffer.
> 
> Currently, the lifecycle of DrawingBuffer is different from it of
> WebGraphicsContext3D, so there is so many checks if the context is valid.
> This complexity is not necessary because DrawingBuffer does not own any
> objects when the context is lost or impossible to be created.
> 
> To be clear the lifecycle, this CL makes DrawingBuffer take ownership of WebGraphicsContext3D.
> 
> The DrawingBuffer creation or resize can fail if the memory is not enough. This
> logic is preserved.
> In detail,
> 1. If it occurs during WebGLRenderingContext creation, we give up creating
> WebGLRenderingContext.
> 2. If it occurs during restoration of lost context, we will try again.
> 3. If it occurs during resizing DrawingBuffer, we slightly ignore, because we
> can reuse different size FBO in this case.
> 
> In addition, this CL fixes two bugs.
> 1. maybeRestoreContext() pretends to success to restore although creating FBO in
> DrawingBuffer fails. As mentioned earlier, we will try again.
> 2. WebGLRenderingContext calls DrawingBuffer::reset() twice during creation,
> because the constructor of DrawingBuffer internally calls reset().
> 
> BUG=344393
> 
> Review URL: https://codereview.chromium.org/163773007

TBR=dongseong.hwang@intel.com

Review URL: https://codereview.chromium.org/184343005

git-svn-id: svn://svn.chromium.org/blink/trunk@168481 bbb929c8-8fbe-4397-9dbb-9b2b20218538