Canvas.toDataURL to use SkBitmap::readPixels to avoid uninitialized memory

Source/core/html/HTMLCanvasElement.cpp

Index: Source/core/html/HTMLCanvasElement.cpp
diff --git a/Source/core/html/HTMLCanvasElement.cpp b/Source/core/html/HTMLCanvasElement.cpp
index a41bd5beb6c08ff3077a3349eed785e68b5293e3..4c6bd64d722fe2fc693610e29db1cccfbf9310e2 100644
--- a/Source/core/html/HTMLCanvasElement.cpp
+++ b/Source/core/html/HTMLCanvasElement.cpp
@@ -469,22 +469,30 @@ String HTMLCanvasElement::toDataURLInternal(const String& mimeType, const double
         return String("data:,");
 
     String encodingMimeType = toEncodingMimeType(mimeType);
-    if (!m_context) {
-        ImageData* imageData = ImageData::create(m_size);
-        ScopedDisposal<ImageData> disposer(imageData);
-        return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
-    }
 
-    if (m_context->is3d()) {
+    if (is3D()) {
         // Get non-premultiplied data because of inaccurate premultiplied alpha conversion of buffer()->toDataURL().
         ImageData* imageData = m_context->paintRenderingResultsToImageData(sourceBuffer);
         ScopedDisposal<ImageData> disposer(imageData);
-        if (imageData)
+        if (imageData) {

[Stephen White, 2015/07/16 19:13:01]

I think this would be clearer and have less code duplication if we did:

ImageData* HTMLCanvasElement::toImageData(...)

which always returns a non-NULL ImageData (transferring ownership). Then
refactor out the ScopedDisposal and the ImageDataBuffer::toDataURL() conversion:

HTMLCanvasElement::toDataURLInternal(...)
{
  ImageData *imageData = toImageData(...);
  ScopedDisposal<ImageData> disposer(imageData);
  return ImageDataBuffer(imageData->size(),
imageData->data()->data()).toDataURL(...);
}

(Would be even nicer if ScopedDisposal had a get() method, so we wouldn't need
two local vars, but that's another issue.)

WDYT?

             return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
+        }
         m_context->paintRenderingResultsToCanvas(sourceBuffer);
+        imageData = ImageData::create(m_size);
+        ScopedDisposal<ImageData> disposer2(imageData);
+        return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
+    }
+
+    ImageData* imageData = ImageData::create(m_size);
+    ScopedDisposal<ImageData> disposer(imageData);
+
+    if (m_context) {
+        ASSERT(m_context->is2d());
+        SkImageInfo imageInfo = SkImageInfo::Make(width(), height(), kRGBA_8888_SkColorType, kUnpremul_SkAlphaType);
+        buffer()->bitmap().readPixels(imageInfo, imageData->data()->data(), imageInfo.minRowBytes(), 0, 0);
     }
 
-    return buffer()->toDataURL(encodingMimeType, quality);
+    return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
 }
 
 String HTMLCanvasElement::toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState) const