Fix warnings on Win64.

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index dc903cd6afc7181334bc4afebcc3d1923fb57c60..9d7b34e7cadf2e335f0d27992c7855d0f9019e7a 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -60,7 +60,7 @@ class UTF8Buffer {
 
   int pos() const {
     ASSERT_NOT_NULL(data_);
-    return cursor_ - data_;
+    return static_cast<int>(cursor_ - data_);
   }
 
   char* data() const { return data_; }
@@ -73,7 +73,7 @@ class UTF8Buffer {
 
   int Capacity() const {
     ASSERT_NOT_NULL(data_);
-    return (limit_ - data_) + unibrow::Utf8::kMaxEncodedSize;
+    return static_cast<int>(limit_ - data_) + unibrow::Utf8::kMaxEncodedSize;
   }
 
   static char* ComputeLimit(char* data, int capacity) {