Android GlRectDrawer: Add fragment shader for RGB(A) textures

Add third shader type for RGB(A) and refactor according to the Rule of three.

BUG=webrtc:4742
R=hbos@webrtc.org

Review URL: https://codereview.webrtc.org/1311093005 .

Cr-Commit-Position: refs/heads/master@{#9843}
1 file changed