Update gradient colorizers to take coords instead of colors.

Gradient layout FPs were passing a position to their colorizers via
sk_InColor.x. This worked, but it makes more sense to pass coordinates
to children by sampling the child at explicit coordinates.

Change-Id: I60520f2e54e04bc9c4d8562e6b2256b95e0de5b4
Bug: skia:10548
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/307217
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 12ff519..7b669ea 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2101,8 +2101,10 @@
   test_app("fuzz") {
     sources = [
       "fuzz/Fuzz.cpp",
+      "fuzz/Fuzz.h",
       "fuzz/FuzzCanvas.cpp",
       "fuzz/FuzzCommon.cpp",
+      "fuzz/FuzzCommon.h",
       "fuzz/FuzzCreateDDL.cpp",
       "fuzz/FuzzDrawFunctions.cpp",
       "fuzz/FuzzEncoders.cpp",
@@ -2476,6 +2478,7 @@
         "tools/viewer/TouchGesture.cpp",
         "tools/viewer/TouchGesture.h",
         "tools/viewer/Viewer.cpp",
+        "tools/viewer/Viewer.h",
       ]
       libs = []