Clamp Mac theme painting to reasonable large bounds.

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

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #include "platform/mac/LocalCurrentGraphicsContext.h"
 
 #include <AppKit/NSGraphicsContext.h>
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/mac/ThemeMac.h"
 #include "platform_canvas.h"
 
 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,
                       m_inflatedDirtyRect,
                       deviceScaleFactor)
 {
     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);
     }
 
     CGContextRef cgContext = this->cgContext();
     if (cgContext == [[NSGraphicsContext currentContext] graphicsPort]) {
         m_savedNSGraphicsContext = 0;
         return;
     }
 
     m_savedNSGraphicsContext = [[NSGraphicsContext currentContext] retain];
@@ skipping 15 matching lines @@
 CGContextRef LocalCurrentGraphicsContext::cgContext()
 {
     // This synchronizes the CGContext to reflect the current SkCanvas state.
     // The implementation may not return the same CGContext each time.
     CGContextRef cgContext = m_skiaBitLocker.cgContext();
 
     return cgContext;
 }
 
 }