Make OffscreenCanvas resizeable

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp

Index: third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
index 4599d147eaff4bf69836dff08758138327d80ca2..f5dc56f1ab7224d176d08aa43a23f8c1d9330bfc 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
@@ -100,6 +100,11 @@ bool OffscreenCanvasRenderingContext2D::hasImageBuffer() const {
   return !!m_imageBuffer;
 }
 
+void OffscreenCanvasRenderingContext2D::reset() {
+  m_imageBuffer = nullptr;

[xlai (Olivia), 2016/11/21 16:26:57]

This function's implementation doesn't look correct.

Once offscreenCanvas'size is changed, the existing image buffer of its 2d
context is set to nullpointer, means everything that has drawn to 2d context so
far is lost. 

[xlai (Olivia), 2016/11/21 19:56:17]

Ah I just realize that the image buffer (with a new size) is always recreated in
every call to transferToStaticBitmapImage() if it is nullptr. 

+  BaseRenderingContext2D::reset();
+}
+
 ImageBuffer* OffscreenCanvasRenderingContext2D::imageBuffer() const {
   if (!m_imageBuffer) {
     IntSize surfaceSize(width(), height());