More Windows 64b compilation warning fixes

https://codereview.chromium.org/47513017/



git-svn-id: http://skia.googlecode.com/svn/trunk@12337 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/gl/GrGLProgramDesc.cpp b/src/gpu/gl/GrGLProgramDesc.cpp
index d958742..e655210 100644
--- a/src/gpu/gl/GrGLProgramDesc.cpp
+++ b/src/gpu/gl/GrGLProgramDesc.cpp
@@ -105,7 +105,7 @@
         memset(desc->header(), 0, kHeaderSize);
     }
     // write the key length
-    *desc->atOffset<uint32_t, kLengthOffset>() = newKeyLength;
+    *desc->atOffset<uint32_t, kLengthOffset>() = SkToU32(newKeyLength);
 
     KeyHeader* header = desc->header();
     EffectKey* effectKeys = desc->effectKeys();