Enable ClangTidy check llvm-namespace-comment.

This fixes a large number of SkSL namespaces which were labeled as if
they were anonymous, and also a handful of other mislabeled namespaces.
Missing namespace-end comments have been added throughout.
A number of diffs are just indentation-related (adjusting 1- or 3-
space indents to 2-space).

Change-Id: I6c62052a0d3aea4ae12ca07e0c2a8587b2fce4ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/308503
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
diff --git a/gm/complexclip.cpp b/gm/complexclip.cpp
index 9960845..5bdec62 100644
--- a/gm/complexclip.cpp
+++ b/gm/complexclip.cpp
@@ -207,7 +207,7 @@
 DEF_GM(return new ComplexClipGM(true, false, true);)
 DEF_GM(return new ComplexClipGM(true, true, false);)
 DEF_GM(return new ComplexClipGM(true, true, true);)
-}
+}  // namespace skiagm
 
 DEF_SIMPLE_GM(clip_shader, canvas, 840, 650) {
     auto img = GetResourceAsImage("images/yellow_rose.png");
@@ -343,7 +343,7 @@
     canvas->drawString(banner.c_str(), 20.f, -30.f, kFont, SkPaint());
 };
 
-} // anonymous
+}  // namespace
 
 DEF_SIMPLE_GM(clip_shader_persp, canvas, 1370, 1030) {
     // Each draw has a clipShader(image-shader), a clipShader(gradient-shader), a concat(persp-mat),