Second wave of Win64 warning cleanup

src/pdf/SkPDFResourceDict.cpp

Index: src/pdf/SkPDFResourceDict.cpp
===================================================================
--- src/pdf/SkPDFResourceDict.cpp	(revision 11775)
+++ src/pdf/SkPDFResourceDict.cpp	(working copy)
@@ -65,7 +65,7 @@
 
     // Actual sub-dicts will be lazily added later
     fTypes.setCount(kResourceTypeCount);
-    for (size_t i=0; i < kResourceTypeCount; i++) {
+    for (int i=0; i < kResourceTypeCount; i++) {
         fTypes[i] = NULL;
     }
 }