Make OffscreenCanvas resizeable

third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/canvas2d/BaseRenderingContext2D.h"
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "core/css/cssom/CSSURLImageValue.h"
@@ skipping 90 matching lines @@
     CHECK(currState->get());
     c->setMatrix(SkMatrix::I());
     currState->get()->playbackClips(c);
     c->setMatrix(affineTransformToSkMatrix(currState->get()->transform()));
     c->save();
   }
   c->restore();
   validateStateStack();
 }
 
+void BaseRenderingContext2D::unwindStateStack() {

[Justin Novosad, 2016/11/16 22:58:18]

code moved from CanvasRenderingContext2D.cpp

+  if (size_t stackSize = m_stateStack.size()) {
+    if (SkCanvas* skCanvas = existingDrawingCanvas()) {
+      while (--stackSize)
+        skCanvas->restore();
+    }
+  }
+}
+
+void BaseRenderingContext2D::reset() {
+  validateStateStack();
+  unwindStateStack();
+  m_stateStack.resize(1);
+  m_stateStack.first() = CanvasRenderingContext2DState::create();
+  m_path.clear();
+  if (SkCanvas* c = existingDrawingCanvas()) {
+    // The canvas should always have an initial/unbalanced save frame, which
+    // we use to reset the top level matrix and clip here.
+    DCHECK_EQ(c->getSaveCount(), 2);
+    c->restore();
+    c->save();
+    DCHECK(c->getTotalMatrix().isIdentity());
+#if DCHECK_IS_ON()
+    SkIRect clipBounds;
+    DCHECK(c->getClipDeviceBounds(&clipBounds));
+    DCHECK(clipBounds == c->imageInfo().bounds());
+#endif
+  }
+  validateStateStack();
+}
+
 static inline void convertCanvasStyleToUnionType(
     CanvasStyle* style,
     StringOrCanvasGradientOrCanvasPattern& returnValue) {
   if (CanvasGradient* gradient = style->getCanvasGradient()) {
     returnValue.setCanvasGradient(gradient);
     return;
   }
   if (CanvasPattern* pattern = style->getCanvasPattern()) {
     returnValue.setCanvasPattern(pattern);
     return;
@@ skipping 1862 matching lines @@
       ExpensiveCanvasHeuristicParameters::ShadowFixedCost[index] *
           m_usageCounters.numBlurredShadows +
       ExpensiveCanvasHeuristicParameters::
               ShadowVariableCostPerAreaTimesShadowBlurSquared[index] *
           m_usageCounters.boundingBoxAreaTimesShadowBlurSquared;
 
   return basicCostOfDrawCalls + fillTypeAdjustment + shadowAdjustment;
 }
 
 }  // namespace blink