use NewUninitialized, cheaper than NewWithMalloc

chrome/browser/android/thumbnail/thumbnail_store.cc

Index: chrome/browser/android/thumbnail/thumbnail_store.cc
diff --git a/chrome/browser/android/thumbnail/thumbnail_store.cc b/chrome/browser/android/thumbnail/thumbnail_store.cc
index a1652d15326d1e660e0ab07e85a3a99a7664d82d..3c9a25c485c01f3fd107358ee472a19bd5f090be 100644
--- a/chrome/browser/android/thumbnail/thumbnail_store.cc
+++ b/chrome/browser/android/thumbnail/thumbnail_store.cc
@@ -569,7 +569,7 @@ void ThumbnailStore::CompressionTask(
                                          kUnknown_SkColorType,
                                          kUnpremul_SkAlphaType);
     skia::RefPtr<SkData> etc1_pixel_data = skia::AdoptRef(
-        SkData::NewFromMalloc(new uint8_t[encoded_bytes], encoded_bytes));
+        SkData::NewUninitialized(encoded_bytes));
     skia::RefPtr<SkMallocPixelRef> etc1_pixel_ref = skia::AdoptRef(
         SkMallocPixelRef::NewWithData(info, 0, NULL, etc1_pixel_data.get()));

[f(malita), 2014/09/12 11:49:59]

Is this safe? Looks like SkMallocPixelRef is ref-ing etc1_pixel_data before we
write data, but per SkData::NewUninitialized() docs

"The caller should call writable_data()  to write into the buffer, but this must
be done before another ref() is made"

[f(malita), 2014/09/12 11:54:34]

I see it's just writable_data() asserting it gets called before ref-ing, so if
we're not using that at all it should be OK.

non-owner lgtm

[reed1, 2014/09/12 18:00:08]

Yes, the existing code is tricky that way, but since they're not calling
data->data() we won't get an assert.

 
@@ -682,13 +682,12 @@ bool ReadFromFile(base::File& file,
     return false;
   }
 
-  skia::RefPtr<SkData> etc1_pixel_data;
   int data_size = etc1_get_encoded_data_size(raw_width, raw_height);
-  scoped_ptr<uint8_t[]> raw_data =
-      scoped_ptr<uint8_t[]>(new uint8_t[data_size]);
+  skia::RefPtr<SkData> etc1_pixel_data =
+      skia::AdoptRef(SkData::NewUninitialized(data_size));
 
   int pixel_bytes_read = file.ReadAtCurrentPos(
-      reinterpret_cast<char*>(raw_data.get()),
+      reinterpret_cast<char*>(etc1_pixel_data->writable_data()),
       data_size);
 
   if (pixel_bytes_read != data_size)
@@ -699,9 +698,6 @@ bool ReadFromFile(base::File& file,
                                        kUnknown_SkColorType,
                                        kUnpremul_SkAlphaType);
 
-  etc1_pixel_data = skia::AdoptRef(
-      SkData::NewFromMalloc(raw_data.release(), data_size));
-
   *out_pixels = skia::AdoptRef(
       SkMallocPixelRef::NewWithData(info,
                                     0,