DeferredImageDecoder: early-out onGetYUV8Planes when possible

third_party/WebKit/Source/platform/graphics/DeferredImageDecoder.cpp

Index: third_party/WebKit/Source/platform/graphics/DeferredImageDecoder.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/DeferredImageDecoder.cpp b/third_party/WebKit/Source/platform/graphics/DeferredImageDecoder.cpp
index e5a1c88f4df1115947612dde313db1ccba1d5f38..ac7e784e0a0bab87f9cb46f7260ad6cca502aaaf 100644
--- a/third_party/WebKit/Source/platform/graphics/DeferredImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/graphics/DeferredImageDecoder.cpp
@@ -26,6 +26,7 @@
 #include "config.h"
 #include "platform/graphics/DeferredImageDecoder.h"
 
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/DecodingImageGenerator.h"
 #include "platform/graphics/FrameData.h"
 #include "platform/graphics/ImageDecodingStore.h"
@@ -58,6 +59,7 @@ DeferredImageDecoder::DeferredImageDecoder(PassOwnPtr<ImageDecoder> actualDecode
     , m_actualDecoder(actualDecoder)
     , m_repetitionCount(cAnimationNone)
     , m_hasColorProfile(false)
+    , m_canYUVDecode(false)
 {
 }
 
@@ -214,9 +216,13 @@ void DeferredImageDecoder::activateLazyDecoding()
 {
     if (m_frameGenerator)
         return;
+
     m_size = m_actualDecoder->size();
     m_filenameExtension = m_actualDecoder->filenameExtension();
+    // JPEG images support YUV decoding: other decoders do not, WEBP could in future.
+    m_canYUVDecode = RuntimeEnabledFeatures::decodeToYUVEnabled() && (m_filenameExtension == "jpg");
     m_hasColorProfile = m_actualDecoder->hasColorProfile();
+
     const bool isSingleFrame = m_actualDecoder->repetitionCount() == cAnimationNone || (m_allDataReceived && m_actualDecoder->frameCount() == 1u);
     m_frameGenerator = ImageFrameGenerator::create(SkISize::Make(m_actualDecoder->decodedSize().width(), m_actualDecoder->decodedSize().height()), m_data, m_allDataReceived, !isSingleFrame);
 }
@@ -276,6 +282,7 @@ PassRefPtr<SkImage> DeferredImageDecoder::createFrameImageAtIndex(size_t index,
         return nullptr;
 
     generator->setGenerationId(image->uniqueID());
+    generator->setCanYUVDecode(m_canYUVDecode);

[scroggo_chromium, 2015/12/07 16:40:02]

Can we instead set this in DecodingImageGenerator's constructor? Then we can
make its m_canYUVDecode const and take away the setter (it only appears to be
called at creation time).

[Noel Gordon, 2015/12/08 01:40:08]

Yeah possible, though I noted the setup / construction / ownership of this
generator-and-image-combo here is all a bit fraught (complicated).

I settled on having a setCanYUVDecode setter here to try and make the whole
thing a little clearer to me; dunno if I succeeded.

     return image.release();
 }