Optimize textures binding.

The renderer is still changing textures' wrap modes every time, this will require
a latter optimization.

Change-Id: I3eb92cb8c886c4a692b7f0ca759911f9371d4d2c
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index 5667229..235931c 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -311,6 +311,9 @@
     // Used to draw textured quads
     TextureVertex mDrawTextureVertices[4];
 
+    // Current texture state
+    GLuint mLastTexture;
+
     // Last known blend state
     bool mBlend;
     GLenum mLastSrcMode;