Skia: Track the fIsWrapped separately so that we delete correctly

GrGlTextureRenderTarget inherits virtually from both GrGlRenderTarget and
GrGLTexture, which both have a 'wrap' flag.  The passed in wrap setting could
be different for the two base classes, but since it's virtually inherited,
they share the same flag, so they're either both on, or both off.

As a result, we fail to delete the frambuffer.

To fix this, we now keep a separate isWrapped flag for GrGlRenderTarget.

BUG=437998

Review URL: https://codereview.chromium.org/791493003