Framebuffer clear() needs to consider the situation some draw buffers are disabled.

This is when we expose DrawBuffers extension.

BUG=376951
TEST=the attached test case, webgl conformance
R=kbr@chromium.org,bajones@chromium.org

Review URL: https://codereview.chromium.org/315283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275338 0039d316-1c4b-4281-b951-d872f2087c98
void GLES2DecoderImpl::DoVertexAttrib2f(GLuint index, GLfloat v0, GLfloat v1) {
  GLfloat v[4] = { v0, v1, 0.0f, 1.0f, };
  if (SetVertexAttribValue("glVertexAttrib2f", index, v)) {
    glVertexAttrib2f(index, v0, v1);
  }
}

void GLES2DecoderImpl::DoVertexAttrib2f(GLuint index, GLfloat v0, GLfloat v1) {
  GLfloat v[4] = { v0, v1, 0.0f, 1.0f, };
  if (SetVertexAttribValue("glVertexAttrib2f", index, v)) {
    glVertexAttrib2f(index, v0, v1);
  }
}
