Revert of Command Buffer: read pixels into pixel pack buffer

gpu/command_buffer/client/gles2_implementation.cc

Index: gpu/command_buffer/client/gles2_implementation.cc
diff --git a/gpu/command_buffer/client/gles2_implementation.cc b/gpu/command_buffer/client/gles2_implementation.cc
index cebd672bef2b4beba173c48a44d9631844dd34da..587a5db07d5513758a194ac285f3bd7f0a1d1620 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -3541,10 +3541,10 @@
   }
 
   if (bound_pixel_pack_buffer_) {
-    GLuint offset = ToGLuint(pixels);
-    helper_->ReadPixels(
-        xoffset, yoffset, width, height, format, type, 0, offset, 0, 0, false);
-    CheckGLError();
+    // TODO(zmo): Need to handle the case of reading into a PIXEL_PACK_BUFFER
+    // in ES3. For now, generate a GL error.
+    SetGLError(GL_INVALID_OPERATION, "glReadPixels",
+               "ReadPixels to a pixel pack buffer isn't implemented");
     return;
   }