Fix dead-lock issue attempting to decode

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

Index: third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp b/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
index 160ecd439c10e0ffc56a7cbc3f685abdacd469c0..584125a61481f4410339c05572a29e8b920500d1 100644
--- a/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
+++ b/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
@@ -54,7 +54,17 @@ SkData* DecodingImageGenerator::onRefEncodedData(GrContext* ctx)
 {
     TRACE_EVENT0("blink", "DecodingImageGenerator::refEncodedData");
 
-    return m_allDataReceived ? m_data->getAsSkData().leakRef() : nullptr;
+    // The GPU only wants the data if it has all been received, since the GPU
+    // only wants a complete texture. getAsSkData() may require copying, so
+    // skip it and just return nullptr to avoid a slowdown. (See
+    // crbug.com/568016 for details about such a slowdown.)

[f(malita), 2016/06/29 17:38:37]

It seems a bit fragile to tweak this implementation for internal Skia semantics.
 Would it make sense to add a "bool requireCompleteData" param to
onRefEncodedData() at some point?

[reed1, 2016/06/29 17:57:45]

agreed, seems fragile. Can you imagine other ways to address this longer term?
- explicit flags sent to this api?
- diff API reporting if the generator is "complete"?
- other?

[scroggo_chromium, 2016/06/29 19:21:21]

Tracking with a bug: skbug.com/5485

[scroggo_chromium, 2016/06/29 19:21:21]

Agreed. Added a TODO.
Possibly. Prior to reed@'s landing of crrev.com/1970773002, we discussed many
options for how to do this better, and weren't happy with any of them. For the
moment, we decided to remove the call that was inefficient, and bring it back
once it actually gets used.

+    if (ctx && !m_allDataReceived)
+        return nullptr;
+
+    // Other clients are serializers, which want the data even if it requires
+    // copying, and even if the data is incomplete. (Otherwise they would
+    // potentially need to decode the partial image in order to re-encode it.)
+    return m_data->getAsSkData().leakRef();
 }
 
 bool DecodingImageGenerator::onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, SkPMColor table[], int* tableCount)