retry³ absl

This merges the two CLs we've been considering,

    1) the first attempt,
       https://skia-review.googlesource.com/c/skia/+/286070;
    2) the roll to latest Abseil LTS branch,
       https://skia-review.googlesource.com/c/skia/+/323076.

(See also the second attempt,
https://skia-review.googlesource.com/c/skia/+/322976.)

We'll need this working in Google3 or punt like we have for Android.

Bug: skia:10165
Cq-Include-Trybots: luci.skia.skia.primary:Canary-G3
Change-Id: Ifb42c1bb2c5e70848208d17b841cdb67bd36e182
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/323158
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/DEPS b/DEPS
index 01e8056..e476c62 100644
--- a/DEPS
+++ b/DEPS
@@ -7,6 +7,7 @@
 deps = {
   "buildtools"                            : "https://chromium.googlesource.com/chromium/buildtools.git@505de88083136eefd056e5ee4ca0f01fe9b33de8",
   "common"                                : "https://skia.googlesource.com/common.git@9737551d7a52c3db3262db5856e6bcd62c462b92",
+  "third_party/externals/abseil-cpp"      : "https://chromium.googlesource.com/external/github.com/abseil/abseil-cpp.git@b56cbdd23834a65682c0b46f367f8679e83bc894",
   "third_party/externals/angle2"          : "https://chromium.googlesource.com/angle/angle.git@77e3d0ae97b620d8980049f0c8572a981bd2963d",
   "third_party/externals/d3d12allocator"  : "https://skia.googlesource.com/external/github.com/GPUOpen-LibrariesAndSDKs/D3D12MemoryAllocator.git@169895d529dfce00390a20e69c2f516066fe7a3b",
   # Dawn requires jinja2 and markupsafe for the code generator, and glslang and shaderc for SPIRV compilation.