Fix !defined(SK_XML) builds

Add guards for dependent code.

TBR=
Change-Id: I49c0c90a2defc6f39589721f95562e9e0f17db13
Reviewed-on: https://skia-review.googlesource.com/144610
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>

BUILD.gn

@@ -1674,15 +1674,17 @@ if (skia_enable_tools) {
     ]
   }
 
-  test_app("create_test_font_color") {
-    sources = [
-      "tools/fonts/create_test_font_color.cpp",
-    ]
-    deps = [
-      ":flags",
-      ":skia",
-      ":tool_utils",
-    ]
+  if (skia_use_expat) {
+    test_app("create_test_font_color") {
+      sources = [
+        "tools/fonts/create_test_font_color.cpp",
+      ]
+      deps = [
+        ":flags",
+        ":skia",
+        ":tool_utils",
+      ]
+    }
   }
 
   test_app("get_images_from_skps") {

tools/skpbench/skpbench.cpp

@@ -533,6 +533,7 @@ static sk_sp<SkPicture> create_skp_from_svg(SkStream* stream, const char* filena
     return recorder.finishRecordingAsPicture();
 #endif
     exitf(ExitErr::kData, "SK_XML is disabled; cannot open svg file %s", filename);
+    return nullptr;
 }
 
 bool mkdir_p(const SkString& dirname) {

tools/viewer/SvgSlide.cpp

@@ -7,6 +7,8 @@
 
 #include "SvgSlide.h"
 
+#if defined(SK_XML)
+
 #include "SkCanvas.h"
 #include "SkStream.h"
 #include "SkSVGDOM.h"
@@ -41,3 +43,5 @@ void SvgSlide::draw(SkCanvas* canvas) {
         fDom->render(canvas);
     }
 }
+
+#endif // SK_XML

tools/viewer/Viewer.cpp

@@ -530,10 +530,12 @@ void Viewer::initSlides() {
                 return sk_make_sp<SkottieSlide>(name, path);}
         },
 #endif
+#if defined(SK_XML)
         { ".svg", "svg-dir", FLAGS_svgs,
             [](const SkString& name, const SkString& path) -> sk_sp<Slide> {
                 return sk_make_sp<SvgSlide>(name, path);}
         },
+#endif
 #if !(defined(SK_BUILD_FOR_WIN) && defined(__clang__))
         { ".nima", "nima-dir", FLAGS_nimas,
             [](const SkString& name, const SkString& path) -> sk_sp<Slide> {