Temporarily name last supported shader tilemode

This is needed to enable the starter impl CL for decal:
https://skia-review.googlesource.com/c/skia/+/107420

Bug: skia:7638
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I00638d8f54b48e8a0b04b10c2c0a556e0c6023ae
Reviewed-on: https://chromium-review.googlesource.com/922804Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Mike Reed <reed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537198}

cc/paint/paint_op_reader.cc

@@ -53,7 +53,8 @@ bool IsValidPaintShaderType(PaintShader::Type type) {
 }
 
 bool IsValidSkShaderTileMode(SkShader::TileMode mode) {
-  return mode < SkShader::kTileModeCount;
+  // When Skia adds Decal, update this (skbug.com/7638)
+  return mode <= SkShader::kMirror_TileMode;
 }
 
 bool IsValidPaintShaderScalingBehavior(PaintShader::ScalingBehavior behavior) {