SkStream: remove some WStream functions from public api

move functions to SkStringPriv.h

also add SkStrAppendU32Hex() function, and re-write
SkString::insertHex() to use SkStrAppendU32Hex.

add unit tests.

Change-Id: Ieda98fb4106db71565b607e593713a91a5ddd892
Reviewed-on: https://skia-review.googlesource.com/151986
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/src/pdf/SkPDFMakeToUnicodeCmap.cpp b/src/pdf/SkPDFMakeToUnicodeCmap.cpp
index f4789a8..42e35f5 100644
--- a/src/pdf/SkPDFMakeToUnicodeCmap.cpp
+++ b/src/pdf/SkPDFMakeToUnicodeCmap.cpp
@@ -8,6 +8,7 @@
 #include "SkPDFMakeToUnicodeCmap.h"
 
 #include "SkPDFUtils.h"
+#include "SkStreamPriv.h"
 #include "SkTo.h"
 #include "SkUTF.h"
 
@@ -88,7 +89,7 @@
     for (size_t i = 0; i < bfchar.size(); i += 100) {
         int count = SkToInt(bfchar.size() - i);
         count = SkMin32(count, 100);
-        cmap->writeDecAsText(count);
+        SkWStreamWriteDecAsText(cmap, count);
         cmap->writeText(" beginbfchar\n");
         for (int j = 0; j < count; ++j) {
             cmap->writeText("<");
@@ -108,7 +109,7 @@
     for (size_t i = 0; i < bfrange.size(); i += 100) {
         int count = SkToInt(bfrange.size() - i);
         count = SkMin32(count, 100);
-        cmap->writeDecAsText(count);
+        SkWStreamWriteDecAsText(cmap, count);
         cmap->writeText(" beginbfrange\n");
         for (int j = 0; j < count; ++j) {
             cmap->writeText("<");