The old implementation would try to keep recording draw commands to
the same framebuffer write operation even if the vertex array buffer
data changed. This would lead to a broken dependency graph. Fix this
by forcing any current render operations to create a new node in this
case, giving a correct command graph.

Old design:

- render (creates a CommandBufferNode A)
- update buffer (creates a CommandBufferNode B which happens after A)
- render (to CommandBuffer A, and gives a circular dependency with B)

New design

- render (CommandBufferNode A)
- update buffer (CommandBufferNode B, happens after A)
- render (CommandBufferNode C, happens after B)

This also renames some methods to try to clarify them.

Bug: angleproject:2350

Change-Id: I6559bed4ed3f58f68771662422c5bef6a505282b
Reviewed-on: https://chromium-review.googlesource.com/907416Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>