Adds filter support for offscreen canvas

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp

Index: third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
diff --git a/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp b/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
index c44f731220e1586fb447203da300f79dff3e1419..57e405eba1a1298b0d4318878acd5abe834d81f7 100644
--- a/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
+++ b/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
@@ -295,7 +295,7 @@ SkImageFilter* CanvasRenderingContext2DState::getFilter(Element* styleResolution
         return nullptr;
 
     // StyleResolverState cannot be used in frame-less documents.
-    if (!styleResolutionHost->document().frame())
+    if (styleResolutionHost && !styleResolutionHost->document().frame())
         return nullptr;
 
     if (!m_resolvedFilter) {
@@ -303,11 +303,21 @@ SkImageFilter* CanvasRenderingContext2DState::getFilter(Element* styleResolution
         // Must set font in case the filter uses any font-relative units (em, ex)
         filterStyle->setFont(m_fontForFilter);
 
-        StyleResolverState resolverState(styleResolutionHost->document(), styleResolutionHost, filterStyle.get());
-        resolverState.setStyle(filterStyle);
+        if (styleResolutionHost) {
+            StyleResolverState resolverState(styleResolutionHost->document(), styleResolutionHost, filterStyle.get());
+            resolverState.setStyle(filterStyle);
+
+            StyleBuilder::applyProperty(CSSPropertyFilter, resolverState, *m_filterValue);
+            resolverState.loadPendingResources();
+        } else {
+            StyleResolverState resolverState(filterStyle.get());
+            resolverState.setStyle(filterStyle);
+
+            StyleBuilder::applyProperty(CSSPropertyFilter, resolverState, *m_filterValue);
+            resolverState.loadPendingResources();
+        }
+
 
-        StyleBuilder::applyProperty(CSSPropertyFilter, resolverState, *m_filterValue);
-        resolverState.loadPendingResources();
         FilterEffectBuilder* filterEffectBuilder = FilterEffectBuilder::create();
 
         // We can't reuse m_fillPaint and m_strokePaint for the filter, since these incorporate
@@ -325,7 +335,7 @@ SkImageFilter* CanvasRenderingContext2DState::getFilter(Element* styleResolution
         if (FilterEffect* lastEffect = filterEffectBuilder->lastEffect()) {
             lastEffect->determineMaximumEffectRect(DetermineMaxEffectRectNone);
             m_resolvedFilter = SkiaImageFilterBuilder::build(lastEffect, ColorSpaceDeviceRGB);
-            if (m_resolvedFilter) {
+            if (styleResolutionHost && m_resolvedFilter) {
                 updateFilterReferences(toHTMLCanvasElement(styleResolutionHost), context, filterStyle->filter());
                 if (lastEffect->originTainted())
                     context->setOriginTainted();