Determine if OffscreenCanvas is paintable in different rendering contexts

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

Index: third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
diff --git a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
index 316d340d0bf159ad50a06f8032c4ad03143ffdbf..526b9fb656f544c1aa9ecb33fb014edb31cc774f 100644
--- a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
+++ b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
@@ -8,6 +8,7 @@
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
+#include "platform/graphics/ImageBuffer.h"
 #include "wtf/MathExtras.h"
 #include <memory>
 
@@ -109,6 +110,13 @@ bool OffscreenCanvas::originClean() const
     return m_originClean && !m_disableReadingFromCanvas;
 }
 
+bool OffscreenCanvas::isPaintable() const
+{
+    if (!m_context)
+        return ImageBuffer::canCreateImageBuffer(m_size);

[Ken Russell (switch to Gerrit), 2016/08/19 20:31:01]

How reliable is this query, and how much does that matter?

This might return true but fail to allocate the image buffer for several
reasons:

 - It tries to allocate an OpenGL texture but the canvas's width or height is
over the OpenGL maximum texture limit (I'm not sure whether this can happen or
whether e.g. Skia would fall back to software in this case)
 - It might run out of CPU-side memory if the ImageBuffer's backing store is
allocated there
 - More?

+    return m_context->isPaintable();
+}
+
 DEFINE_TRACE(OffscreenCanvas)
 {
     visitor->trace(m_context);