Adds a DynamicState struct to GrPipeline that has a field for the
scissor rect. Eventually this should become the only way to specify a
scissor rectangle and may grow to contain more fields. Adds an array of
DynamicStates to GrGpuCommandBuffer::draw and implements support in GL
and Vulkan.
Bug: skia:
Change-Id: If5aebbf9da5d192acf7e68e7def4674ffc7ec310
Reviewed-on: https://skia-review.googlesource.com/18510
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
