If glMapBufferRange is called with GL_MAP_INVALIDATE_BUFFER_BIT bit set,
caller indicates that it don't care about the previous content. If the
buffer is busy, instead of wait for GPU to finish and then map the
buffer, we should just allocate a new memory and return it.

brawl_stars is hitting this case. With this CL, the frame time is
cutting to half on the pixel device.

Bug: b/175905404
Change-Id: If1220f07ebf53dd28fe6a4732eaba84e2e57598e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2597784Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Charlie Lao <cclao@google.com>