SkStream/Priv cleanups

Replace all callers of SkCopyStreamToStorage with SkCopyStreamToData,
which is simpler and does the same thing.

Remove SkStreamRewindableFromSkStream, which is unused.

BUG=skia:4788
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1604963002

Review URL: https://codereview.chromium.org/1604963002
diff --git a/src/images/SkImageDecoder_libbmp.cpp b/src/images/SkImageDecoder_libbmp.cpp
index 1791623..4a6f71c 100644
--- a/src/images/SkImageDecoder_libbmp.cpp
+++ b/src/images/SkImageDecoder_libbmp.cpp
@@ -9,6 +9,7 @@
 
 #include "bmpdecoderhelper.h"
 #include "SkColorPriv.h"
+#include "SkData.h"
 #include "SkImageDecoder.h"
 #include "SkScaledBitmapSampler.h"
 #include "SkStream.h"
@@ -96,10 +97,13 @@
     // First read the entire stream, so that all of the data can be passed to
     // the BmpDecoderHelper.
 
-    // Allocated space used to hold the data.
-    SkAutoMalloc storage;
+    SkAutoTUnref<SkData> data(SkCopyStreamToData(stream));
+    if (!data) {
+        return kFailure;
+    }
+
     // Byte length of all of the data.
-    const size_t length = SkCopyStreamToStorage(&storage, stream);
+    const size_t length = data->size();
     if (0 == length) {
         return kFailure;
     }
@@ -111,7 +115,7 @@
     {
         image_codec::BmpDecoderHelper helper;
         const int max_pixels = 16383*16383; // max width*height
-        if (!helper.DecodeImage((const char*)storage.get(), length,
+        if (!helper.DecodeImage((const char*) data->data(), length,
                                 max_pixels, &callback)) {
             return kFailure;
         }
@@ -119,7 +123,7 @@
 
     // we don't need this anymore, so free it now (before we try to allocate
     // the bitmap's pixels) rather than waiting for its destructor
-    storage.free();
+    data.reset(nullptr);
 
     int width = callback.width();
     int height = callback.height();