Restore ETC1 compressed texture support.

Brings back GL ETC1 support and adds Vulkan support as well.

Bug: skia:8684
Change-Id: Ie65da0a3172793081f0e4072f161bfb9b14678bc
Reviewed-on: https://skia-review.googlesource.com/c/179724
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index c34d99a..3eae2ce 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -167,6 +167,7 @@
     "src/utils",
     "src/utils/win",
     "src/xml",
+    "third_party/etc1",
     "third_party/gif",
   ]
 
@@ -950,6 +951,7 @@
     "src/sfnt/SkOTTable_name.cpp",
     "src/sfnt/SkOTUtils.cpp",
     "src/utils/mac/SkStream_mac.cpp",
+    "third_party/etc1/etc1.cpp",
     "third_party/gif/SkGifImageReader.cpp",
   ]
 
@@ -2264,6 +2266,7 @@
         "src/sfnt/SkOTTable_name.cpp",
         "src/sfnt/SkOTUtils.cpp",
         "src/utils/mac/SkStream_mac.cpp",
+        "third_party/etc1/etc1.cpp",
         "third_party/gif/SkGifImageReader.cpp",
       ]
       deps = [