use SkData::NewUninitialized, cheaper than NewFromMalloc

Source/platform/SharedBuffer.cpp

Index: Source/platform/SharedBuffer.cpp
diff --git a/Source/platform/SharedBuffer.cpp b/Source/platform/SharedBuffer.cpp
index f6cf3dc50d0e9f6b4dff0f2da99192fdeadd1e54..6594e7a9997651a24686ef91301fa8b1ee85bfcd 100644
--- a/Source/platform/SharedBuffer.cpp
+++ b/Source/platform/SharedBuffer.cpp
@@ -386,7 +386,8 @@ PassRefPtr<ArrayBuffer> SharedBuffer::getAsArrayBuffer() const
 PassRefPtr<SkData> SharedBuffer::getAsSkData() const
 {
     unsigned bufferLength = size();
-    char* buffer = static_cast<char*>(sk_malloc_throw(bufferLength));
+    SkData* data = SkData::NewUninitialized(bufferLength);
+    char* buffer = static_cast<char*>(data->writable_data());
     const char* segment = 0;
     unsigned position = 0;
     while (unsigned segmentSize = getSomeData(segment, position)) {
@@ -399,7 +400,7 @@ PassRefPtr<SkData> SharedBuffer::getAsSkData() const
         // Don't return the incomplete SkData.
         return nullptr;
     }
-    return adoptRef(SkData::NewFromMalloc(buffer, bufferLength));
+    return adoptRef(data);
 }
 
 bool SharedBuffer::lock()