Enable 64-bit builds on Windows

Encountered compile errors passing 64-bit size_t to
SkIntToScalar and needed to make adjustments to
gm/gradients.cpp and bench/PicturePlaybackBench.cpp.

Verified on my local Linux, Mac, and Windows machines.

As of this change, the skia_arch_width gyp define
actually forces a 32/64-bit build on Linux, Mac, and
Windows.
Review URL: https://codereview.appspot.com/6460112

git-svn-id: http://skia.googlecode.com/svn/trunk@5195 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index eff47bf..b9fa429 100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -85,6 +85,14 @@
             },
           },
         },
+        'conditions' : [
+          ['skia_arch_width == 64', {
+            'msvs_configuration_platform': 'x64'
+          }],
+          ['skia_arch_width == 32', {
+            'msvs_configuration_platform': 'Win32',
+          }],
+        ],
       },
     ],