Clamp Mac theme painting to reasonable large bounds.

third_party/WebKit/Source/platform/mac/LocalCurrentGraphicsContext.mm

Index: third_party/WebKit/Source/platform/mac/LocalCurrentGraphicsContext.mm
diff --git a/third_party/WebKit/Source/platform/mac/LocalCurrentGraphicsContext.mm b/third_party/WebKit/Source/platform/mac/LocalCurrentGraphicsContext.mm
index cb50058ead46f319891930a36e83fdad78b86378..514d07b2916d8ba6bb5215e6359fb41890b38c6c 100644
--- a/third_party/WebKit/Source/platform/mac/LocalCurrentGraphicsContext.mm
+++ b/third_party/WebKit/Source/platform/mac/LocalCurrentGraphicsContext.mm
@@ -27,18 +27,13 @@
 namespace blink {
 
 LocalCurrentGraphicsContext::LocalCurrentGraphicsContext(GraphicsContext& graphicsContext, const IntRect& dirtyRect)
-    : LocalCurrentGraphicsContext(graphicsContext.canvas(), graphicsContext.deviceScaleFactor(), nullptr, dirtyRect)
+    : LocalCurrentGraphicsContext(graphicsContext.canvas(), graphicsContext.deviceScaleFactor(), dirtyRect)
 {
 }
 
-LocalCurrentGraphicsContext::LocalCurrentGraphicsContext(GraphicsContext& graphicsContext, const IntRect* interestRect,
-                                                         const IntRect& dirtyRect)
-    : LocalCurrentGraphicsContext(graphicsContext.canvas(), graphicsContext.deviceScaleFactor(), interestRect, dirtyRect)
-{
-}
+static const int kPixelDistanceToClamp = 4000;
 
-LocalCurrentGraphicsContext::LocalCurrentGraphicsContext(SkCanvas* canvas, float deviceScaleFactor, const IntRect* interestRect,
-                                                         const IntRect& dirtyRect)
+LocalCurrentGraphicsContext::LocalCurrentGraphicsContext(SkCanvas* canvas, float deviceScaleFactor, const IntRect& dirtyRect)
     : m_didSetGraphicsContext(false)
     , m_inflatedDirtyRect(ThemeMac::inflateRectForAA(dirtyRect))
     , m_skiaBitLocker(canvas,
@@ -48,10 +43,10 @@ LocalCurrentGraphicsContext::LocalCurrentGraphicsContext(SkCanvas* canvas, float
     m_savedCanvas = canvas;
     canvas->save();
 
-    bool clipToInterest = interestRect && !interestRect->contains(m_inflatedDirtyRect);
-    if (clipToInterest) {
+    IntRect clampRect(0, 0, kPixelDistanceToClamp, kPixelDistanceToClamp);
+    if (!clampRect.contains(m_inflatedDirtyRect)) {

[chrishtr, 2016/05/05 23:50:58]

I think you need to adjust clampRect by the paint offset. I'd suggest clamping
the size of the dirtyRect with setWidth(min(5000, width())) etc.

[wkorman, 2016/05/06 22:42:55]

Reworked this and added a comment.

         IntRect clippedBounds(m_inflatedDirtyRect);
-        clippedBounds.intersect(*interestRect);
+        clippedBounds.intersect(clampRect);
         canvas->clipRect(clippedBounds, SkRegion::kIntersect_Op);
     }