Disable GLES sampler objects in Skia (#3502)

Forces GLES 3.0 texture sampler units off in all Cobalt builds. Cobalt
rendering code does not use samplers, and mixing Skia state that does,
can result in rendering artifacts like pixelated textures.

b/332330398

third_party/skia/src/gpu/gl/GrGLCaps.cpp

@@ -809,8 +809,13 @@ void GrGLCaps::init(const GrContextOptions& contextOptions,
     } else if (GR_IS_GR_WEBGL(standard)) {
         fSamplerObjectSupport = version >= GR_GL_VER(2,0);
     }
+#if defined(STARBOARD)
+    // Cobalt rendering code cannot interop with sampler objects.
+    fUseSamplerObjects = false;
+#else
     // We currently use sampler objects whenever they are available.
     fUseSamplerObjects = fSamplerObjectSupport;
+#endif
 
     if (GR_IS_GR_GL_ES(standard)) {
         fTiledRenderingSupport = ctxInfo.hasExtension("GL_QCOM_tiled_rendering");