blink: Use external memory allocator in tests using MockImageDecoder.

The caller expects the decoder to populate memory in the allocator if
set, but the MockImageDecoder was not doing this. This causes failures
in MSAN where the memory remains unitinitialized.

Fix MockImageDecoder to respect this expectation.

R=chrishtr@chromium.org

Bug: 877497
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I441095eb3fb89c90cf3b9bf592438cd20b126391
Reviewed-on: https://chromium-review.googlesource.com/1188877
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586090}

third_party/blink/renderer/platform/graphics/image_decoder_wrapper.cc

@@ -165,11 +165,8 @@ bool ImageDecoderWrapper::Decode(ImageDecoderFactory* factory,
 
 // If we decoded into external memory, the bitmap should be backed by the
 // pixels passed to the allocator.
-#if DCHECK_IS_ON()
-  if (!decoder->IsForTesting() && decode_to_external_memory) {
-    DCHECK_EQ(scaled_size_bitmap.getPixels(), pixels_);
-  }
-#endif
+  DCHECK(!decode_to_external_memory ||
+         scaled_size_bitmap.getPixels() == pixels_);
 
   *has_alpha = !scaled_size_bitmap.isOpaque();
   if (!decode_to_external_memory) {

third_party/blink/renderer/platform/graphics/test/mock_image_decoder.h

@@ -107,12 +107,18 @@ class MockImageDecoder : public ImageDecoder {
     return ImageDecoder::FrameBytesAtIndex(index);
   }
 
-  void SetMemoryAllocator(SkBitmap::Allocator*) override {
+  void SetMemoryAllocator(SkBitmap::Allocator* allocator) override {
+    if (frame_buffer_cache_.IsEmpty()) {
+      // Ensure that InitializeNewFrame is called, after parsing if
+      // necessary.
+      if (!FrameCount())
+        return;
+    }
+
+    frame_buffer_cache_[0].SetMemoryAllocator(allocator);
     client_->MemoryAllocatorSet();
   }
 
-  bool IsForTesting() const override { return true; }
-
  private:
   void DecodeSize() override {}
 
@@ -120,6 +126,8 @@ class MockImageDecoder : public ImageDecoder {
 
   void Decode(size_t index) override {
     client_->DecodeRequested();
+    frame_buffer_cache_[index].ClearPixelData();
+    InitializeNewFrame(index);
     frame_buffer_cache_[index].SetStatus(client_->GetStatus(index));
   }
 

third_party/blink/renderer/platform/image-decoders/image_decoder.h

@@ -333,8 +333,6 @@ class PLATFORM_EXPORT ImageDecoder {
   virtual bool DecodeToYUV() { return false; }
   virtual void SetImagePlanes(std::unique_ptr<ImagePlanes>) {}
 
-  virtual bool IsForTesting() const { return false; }
-
  protected:
   ImageDecoder(AlphaOption alpha_option,
                HighBitDepthDecodingOption high_bit_depth_decoding_option,