Fix zoom in CSS paint worklets

third_party/WebKit/Source/modules/csspaint/CSSPaintDefinition.cpp

Index: third_party/WebKit/Source/modules/csspaint/CSSPaintDefinition.cpp
diff --git a/third_party/WebKit/Source/modules/csspaint/CSSPaintDefinition.cpp b/third_party/WebKit/Source/modules/csspaint/CSSPaintDefinition.cpp
index 7da77ddd4e7984fc8c4db12c8f2b3bfb11788796..bb5c2be4a8ffbb707c0531623c0ae8d9bb6bc2dd 100644
--- a/third_party/WebKit/Source/modules/csspaint/CSSPaintDefinition.cpp
+++ b/third_party/WebKit/Source/modules/csspaint/CSSPaintDefinition.cpp
@@ -21,6 +21,17 @@
 
 namespace blink {
 
+namespace {
+
+IntSize adjustToCssSize(const IntSize& size, float zoom)

[Justin Novosad, 2016/07/04 15:45:59]

This name is confusing IMHO. My understanding is that the 'size' argument is the
CSS size, and that we are unzooming it to get some sort of intrinsic size.  The
name suggests the opposite.

[Gleb Lanbin, 2016/07/06 20:36:18]

done, renamed to getSpecifiedSize, according to Object-Sizing Terminology
https://drafts.csswg.org/css-images-3/#sizing-terms, i.e. "...The specified size
of an object is given by CSS, such as through the width and height..."

+{
+    IntSize newSize(size);
+    newSize.scale(1 / zoom);

[Justin Novosad, 2016/07/04 15:45:59]

Due to floating-point precision issues, this arithmetic is not guaranteed to
give the pre-zoom size.  In particular, the results are quite likely to be off
by one since the implementation of IntSize::scale truncates its results (as
opposed to rounding).

[Gleb Lanbin, 2016/07/06 20:36:18]

Done.

+    return newSize;
+}
+
+} // namespace
+
 CSSPaintDefinition* CSSPaintDefinition::create(ScriptState* scriptState, v8::Local<v8::Function> constructor, v8::Local<v8::Function> paint, Vector<CSSPropertyID>& nativeInvalidationProperties, Vector<AtomicString>& customInvalidationProperties)
 {
     return new CSSPaintDefinition(scriptState, constructor, paint, nativeInvalidationProperties, customInvalidationProperties);
@@ -39,7 +50,7 @@ CSSPaintDefinition::~CSSPaintDefinition()
 {
 }
 
-PassRefPtr<Image> CSSPaintDefinition::paint(const LayoutObject& layoutObject, const IntSize& size)
+PassRefPtr<Image> CSSPaintDefinition::paint(const LayoutObject& layoutObject, const IntSize& size, float zoom)
 {
     ScriptState::Scope scope(m_scriptState.get());
 
@@ -55,9 +66,10 @@ PassRefPtr<Image> CSSPaintDefinition::paint(const LayoutObject& layoutObject, co
 
     DCHECK(layoutObject.node());
 
+    const auto cssSize = adjustToCssSize(size, zoom);

[Justin Novosad, 2016/07/04 15:45:58]

abuse of "auto".

[Gleb Lanbin, 2016/07/06 20:36:18]

Done.

     PaintRenderingContext2D* renderingContext = PaintRenderingContext2D::create(
         ImageBuffer::create(wrapUnique(new RecordingImageBufferSurface(size))));
-    PaintSize* paintSize = PaintSize::create(size);
+    PaintSize* paintSize = PaintSize::create(cssSize);
     StylePropertyMap* styleMap = FilteredComputedStylePropertyMap::create(
         CSSComputedStyleDeclaration::create(layoutObject.node()),
         m_nativeInvalidationProperties, m_customInvalidationProperties);
@@ -81,7 +93,7 @@ PassRefPtr<Image> CSSPaintDefinition::paint(const LayoutObject& layoutObject, co
         return nullptr;
     }
 
-    return PaintGeneratedImage::create(renderingContext->imageBuffer()->getPicture(), size);
+    return PaintGeneratedImage::create(renderingContext->imageBuffer()->getPicture(), cssSize);
 }
 
 void CSSPaintDefinition::maybeCreatePaintInstance()