SkPDF: clean up uses of deprecated calls in other SkPDF classes

BUG=skia:3585

Review URL: https://codereview.chromium.org/1107923002
diff --git a/src/pdf/SkPDFBitmap.cpp b/src/pdf/SkPDFBitmap.cpp
index 3b0d38c..29b3bee 100644
--- a/src/pdf/SkPDFBitmap.cpp
+++ b/src/pdf/SkPDFBitmap.cpp
@@ -322,7 +322,7 @@
         result->appendInt(0);
         char shortTableArray[3] = {0, 0, 0};
         SkString tableString(shortTableArray, SK_ARRAY_COUNT(shortTableArray));
-        result->append(new SkPDFString(tableString))->unref();
+        result->appendString(tableString);
         return result;
     }
     result->appendInt(table->count() - 1);  // maximum color index.
@@ -338,7 +338,7 @@
         tablePtr += 3;
     }
     SkString tableString(tableArray, 3 * table->count());
-    result->append(new SkPDFString(tableString))->unref();
+    result->appendString(tableString);
     return result;
 }
 
@@ -362,8 +362,8 @@
     pdfDict.insertInt("Height", fBitmap.height());
     if (fBitmap.colorType() == kIndex_8_SkColorType) {
         SkASSERT(1 == pdf_color_component_count(fBitmap.colorType()));
-        pdfDict.insert("ColorSpace", make_indexed_color_space(
-                                             fBitmap.getColorTable()))->unref();
+        pdfDict.insertObject("ColorSpace",
+                             make_indexed_color_space(fBitmap.getColorTable()));
     } else if (1 == pdf_color_component_count(fBitmap.colorType())) {
         pdfDict.insertName("ColorSpace", "DeviceGray");
     } else {
@@ -371,7 +371,7 @@
     }
     pdfDict.insertInt("BitsPerComponent", 8);
     if (fSMask) {
-        pdfDict.insert("SMask", new SkPDFObjRef(fSMask))->unref();
+        pdfDict.insertObjRef("SMask", SkRef(fSMask.get()));
     }
     pdfDict.insertName("Filter", "FlateDecode");
     pdfDict.insertInt("Length", asset->getLength());