Remove unnecessary style calculations in HTMLCanvasElement

When creating a WebGL canvas, and when allocating a 2D canvas backing,
the implementation was triggering an immediate style calculation
to evaluate the image-redering CSS property.  This CL gets rid of of
these calculations by relying on the fact that if the style is dirty,
it will be updated before the next paint, which will allow for the state
to be corrected after the fact, if necessary.

BUG=585135

Review URL: https://codereview.chromium.org/1674123003

Cr-Commit-Position: refs/heads/master@{#374753}

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

@@ -135,7 +135,6 @@ inline HTMLCanvasElement::HTMLCanvasElement(Document& document)
     , m_didFailToCreateImageBuffer(false)
     , m_imageBufferIsClear(false)
 {
-    setHasCustomStyleCallbacks();
     CanvasMetrics::countCanvasContextUsage(CanvasMetrics::CanvasCreated);
 }
 
@@ -165,24 +164,6 @@ LayoutObject* HTMLCanvasElement::createLayoutObject(const ComputedStyle& style)
     return HTMLElement::createLayoutObject(style);
 }
 
-void HTMLCanvasElement::didRecalcStyle(StyleRecalcChange)
-{
-    SkFilterQuality filterQuality;
-    const ComputedStyle* style = ensureComputedStyle();
-    if (style && style->imageRendering() == ImageRenderingPixelated) {
-        filterQuality = kNone_SkFilterQuality;
-    } else {
-        filterQuality = kLow_SkFilterQuality;
-    }
-
-    if (is3D()) {
-        m_context->setFilterQuality(filterQuality);
-        setNeedsCompositingUpdate();
-    } else if (hasImageBuffer()) {
-        m_imageBuffer->setFilterQuality(filterQuality);
-    }
-}
-
 Node::InsertionNotificationRequest HTMLCanvasElement::insertedInto(ContainerNode* node)
 {
     setIsInCanvasSubtree(true);
@@ -265,10 +246,6 @@ CanvasRenderingContext* HTMLCanvasElement::getCanvasRenderingContext(const Strin
         return nullptr;
 
     if (m_context->is3d()) {
-        document().updateLayoutTreeForNodeIfNeeded(this);
-        const ComputedStyle* style = ensureComputedStyle();
-        if (style)
-            m_context->setFilterQuality(style->imageRendering() == ImageRenderingPixelated ? kNone_SkFilterQuality : kLow_SkFilterQuality);
         updateExternallyAllocatedMemory();
     }
     setNeedsCompositingUpdate();
@@ -458,6 +435,16 @@ void HTMLCanvasElement::paint(GraphicsContext& context, const LayoutRect& r)
     // FIXME: crbug.com/438240; there is a bug with the new CSS blending and compositing feature.
     if (!m_context)
         return;
+
+    const ComputedStyle* style = ensureComputedStyle();
+    SkFilterQuality filterQuality = (style && style->imageRendering() == ImageRenderingPixelated) ? kNone_SkFilterQuality : kLow_SkFilterQuality;
+
+    if (is3D()) {
+        m_context->setFilterQuality(filterQuality);
+    } else if (hasImageBuffer()) {
+        m_imageBuffer->setFilterQuality(filterQuality);
+    }
+
     if (!paintsIntoCanvasBuffer() && !document().printing())
         return;
 
@@ -782,10 +769,6 @@ void HTMLCanvasElement::createImageBufferInternal(PassOwnPtr<ImageBufferSurface>
         return;
     m_imageBuffer->setClient(this);
 
-    document().updateLayoutTreeIfNeeded();
-    const ComputedStyle* style = ensureComputedStyle();
-    m_imageBuffer->setFilterQuality((style && (style->imageRendering() == ImageRenderingPixelated)) ? kNone_SkFilterQuality : kLow_SkFilterQuality);
-
     m_didFailToCreateImageBuffer = false;
 
     updateExternallyAllocatedMemory();

third_party/WebKit/Source/core/html/HTMLCanvasElement.h

@@ -193,7 +193,6 @@ private:
 
     void parseAttribute(const QualifiedName&, const AtomicString&, const AtomicString&) override;
     LayoutObject* createLayoutObject(const ComputedStyle&) override;
-    void didRecalcStyle(StyleRecalcChange) override;
     bool areAuthorShadowsAllowed() const override { return false; }
 
     void reset();