Fix DM build failures:
  - forgot tool_main;
  - skip building where skia_gpu is false;
  - lots of scalar -> int warnings;
  - stray return on a void method;
  - stifle warning about a uint32_t cast to bool

BUG=
R=bungeman@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/26468005

git-svn-id: http://skia.googlecode.com/svn/trunk@11821 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/everything.gyp b/gyp/everything.gyp
index f34b517..8758cc6 100644
--- a/gyp/everything.gyp
+++ b/gyp/everything.gyp
@@ -21,6 +21,10 @@
         }, {
           'dependencies': [ 'debugger.gyp:debugger' ],
         }],
+        # DM assumes you've got a GPU.
+        ['skia_gpu == 1', {
+          'dependencies': [ 'dm.gyp:dm' ],
+        }],
       ],
     },
   ],