Make SkTDArray accessors const-friendly.

This change creates const and non-const versions of SkTDArray::begin(), end(), operator[]() and getAt(). This will keep us from inadvertently changing a const SkTDArray, which the previous signatures allowed.

Review URL: https://chromiumcodereview.appspot.com/12315131

git-svn-id: http://skia.googlecode.com/svn/trunk@7902 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pdf/SkPDFFont.cpp b/src/pdf/SkPDFFont.cpp
index 89b4fc9..3d7902d 100644
--- a/src/pdf/SkPDFFont.cpp
+++ b/src/pdf/SkPDFFont.cpp
@@ -624,7 +624,7 @@
     reset(map);
 }
 
-SkPDFGlyphSetMap::FontGlyphSetPair* SkPDFGlyphSetMap::F2BIter::next() const {
+const SkPDFGlyphSetMap::FontGlyphSetPair* SkPDFGlyphSetMap::F2BIter::next() const {
     if (fIndex >= fMap->count()) {
         return NULL;
     }