Reland "Add stub gpu workaround generators"

This is a reland of 94d25b970b97c68ddd0b4ceb71f2233aac05e6b5

Original change's description:
> Add stub gpu workaround generators
> 
> Like https://chromium-review.googlesource.com/c/chromium/src/+/1005362,
> this patch adds a way for Chrome and Skia to share a set of driver
> workaround names so that they can be turned on by Chrome (or Skia) as
> needed.
> 
> To avoid weird cross-repository dependencies, the generator script is
> duplicated in Skia.
> 
> This patch just adds a few dummy workaround names to make sure the build
> process is working.  The followup to this is to add workaround init
> to GrContext/GrContextOptions and to start implementing individual
> workarounds.
> 
> Implementing these workarounds is to support Chrome's "out of process
> raster" which will use Ganesh without a command buffer, and so will not
> have the workarounds that the command buffer provides.
> 
> Bug: chromium:829614
> Change-Id: I40745a777a95805995991fedb81657ae418b52d9
> Reviewed-on: https://skia-review.googlesource.com/120608
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Adrienne Walker <enne@chromium.org>

Bug: chromium:829614
Change-Id: Idb3309ffa894f7585ee493388b56565e9d4a3101
Reviewed-on: https://skia-review.googlesource.com/122800
Auto-Submit: Adrienne Walker <enne@chromium.org>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 913270d..31035ff 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -86,6 +86,8 @@
   "$_src/gpu/GrDrawOpAtlas.h",
   "$_src/gpu/GrDrawOpTest.cpp",
   "$_src/gpu/GrDrawOpTest.h",
+  "$_src/gpu/GrDriverBugWorkarounds.cpp",
+  "$_src/gpu/GrDriverBugWorkarounds.h",
   "$_src/gpu/GrFixedClip.cpp",
   "$_src/gpu/GrFixedClip.h",
   "$_src/gpu/GrFragmentProcessor.cpp",