Add SurfaceTexture docs for getTransformMatrix.

 * updated to contain the most recent image from the image stream.  This may cause some frames of

 * updated to contain the most recent image from the image stream.  This may cause some frames of

 * the stream to be skipped.

 * the stream to be skipped.

 *

 *

 * <p>When sampling from the texture one should first transform the texture coordinates using the

 * matrix queried via {@link #getTransformMatrix}.  The transform matrix may change each time {@link

 * #updateTexImage} is called, so it should be re-queried each time the texture image is updated.

 * This matrix transforms traditional 2D OpenGL ES texture coordinate column vectors of the form (s,

 * t, 0, 1) where s and t are on the inclusive interval [0, 1] to the proper sampling location in

 * the streamed texture.  This transform compensates for any properties of the image stream source

 * that cause it to appear different from a traditional OpenGL ES texture.  For example, sampling

 * from the bottom left corner of the image can be accomplished by transforming the column vector

 * (0, 0, 0, 1) using the queried matrix, while sampling from the top right corner of the image can

 * be done by transforming (1, 1, 0, 1).

 *

 * <p>The texture object uses the GL_TEXTURE_EXTERNAL_OES texture target, which is defined by the

 * <p>The texture object uses the GL_TEXTURE_EXTERNAL_OES texture target, which is defined by the

 * OES_EGL_image_external OpenGL ES extension.  This limits how the texture may be used.

 * OES_EGL_image_external OpenGL ES extension.  This limits how the texture may be used.

 *

 *