migrate skpdiff to tools

gyp/tools.gyp

Index: gyp/tools.gyp
diff --git a/gyp/tools.gyp b/gyp/tools.gyp
index 5d7c92e6ae470ca082268fae8b29b8141ed88e2b..b359427645660dc98295dae6bd2248566194c7ec 100644
--- a/gyp/tools.gyp
+++ b/gyp/tools.gyp
@@ -21,6 +21,7 @@
         'render_pdfs',
         'render_pictures',
         'skdiff',
+        'skpdiff',
         'skhello',
         'skimage',
       ],
@@ -51,6 +52,54 @@
       ],
     },
     {
+      'target_name': 'skpdiff',
+      'type': 'executable',
+      'sources': [
+        '../tools/skpdiff/skpdiff_main.cpp',
+        '../tools/skpdiff/SkDiffContext.cpp',
+        '../tools/skpdiff/SkImageDiffer.cpp',
+        '../tools/skpdiff/SkPMetric.cpp',
+        '../tools/skpdiff/skpdiff_util.cpp',
+        '../tools/flags/SkCommandLineFlags.cpp',
+      ],
+      'include_dirs': [
+        '../tools/flags'
+      ],
+      'dependencies': [
+        'skia_lib.gyp:skia_lib',
+      ],
+      'cflags': [
+        '-O3',
+      ],
+      'conditions': [
+        ['skia_opencl', {
+          'sources': [
+            '../tools/skpdiff/SkCLImageDiffer.cpp',
+            '../tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp',
+          ],
+          'conditions': [
+            [ 'skia_os == "mac"', {
+              'link_settings': {
+                'libraries': [
+                  '$(SDKROOT)/System/Library/Frameworks/OpenCL.framework',
+                ]
+              }
+            }, {
+              'link_settings': {
+                'libraries': [
+                  '-lOpenCL',
+                ],
+              },
+            }],
+          ],
+        }, { # !skia_opencl
+          'sources': [
+            '../tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp',
+          ],
+        }],
+      ],
+    },
+    {
       'target_name': 'skimagediff',
       'type': 'executable',
       'sources': [