[PDF] Refactor SkPDFFont to enable font/cmap subsetting.

Patch from Arthur Hsu, original CL: http://codereview.appspot.com/4633050/

Review URL: http://codereview.appspot.com/4811049

git-svn-id: http://skia.googlecode.com/svn/trunk@1943 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pdf/SkBitSet.cpp b/src/pdf/SkBitSet.cpp
index f19dd69..c7af832 100755
--- a/src/pdf/SkBitSet.cpp
+++ b/src/pdf/SkBitSet.cpp
@@ -73,12 +73,12 @@
     }
 }
 
-bool SkBitSet::isBitSet(int index) {
+bool SkBitSet::isBitSet(int index) const {
     uint32_t mask = 1 << (index % 32);
     return (*internalGet(index) & mask);
 }
 
-bool SkBitSet::orBits(SkBitSet& source) {
+bool SkBitSet::orBits(const SkBitSet& source) {
     if (fBitCount != source.fBitCount) {
         return false;
     }