Change shared_sources.gni to use relative path

BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("gn/shared_sources.gni")
 
 declare_args() {
   skia_enable_tools = !is_fuchsia && !is_component_build
 
@@ skipping 493 matching lines @@
       "src/ports/SkImageEncoder_CG.cpp",
       "src/ports/SkImageGeneratorCG.cpp",
     ]
     libs += [
       "ApplicationServices.framework",
       "OpenGL.framework",
     ]
   }
 
   if (is_fuchsia) {
-    sources += [ "src/gpu/gl/GrGLCreateNativeInterface_none.cpp" ]
+    sources += [
+      "src/gpu/gl/GrGLCreateNativeInterface_none.cpp",
+      "src/ports/SkDebug_stdio.cpp",
+    ]
   }
 }
 
 skia_h_headers = exec_script("gyp/find.py",
                              [ "*.h" ] + rebase_path(skia_public_includes),
                              "list lines",
                              []) -
                  [
                    rebase_path("include/gpu/gl/GrGLConfig_chrome.h"),
                    rebase_path("include/gpu/vk/GrVkBackendContext.h"),
@@ skipping 288 matching lines @@
     sources = [
       "tools/SkShaper_primitive.cpp",
       "tools/using_skia_and_harfbuzz.cpp",
     ]
     deps = [
       ":skia",
     ]
     testonly = true
   }
 }