WebGL: Restore atomically both WebGraphicsContext3D and DrawingBuffer together.

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 4114 matching lines @@
     for (size_t i = 0; i < m_extensions.size(); ++i) {
         ExtensionTracker* tracker = m_extensions[i];
         tracker->loseExtension();
     }
 
     for (size_t i = 0; i < WebGLExtensionNameCount; ++i)
         m_extensionEnabled[i] = false;
 
     removeAllCompressedTextureFormats();
 
-    if (mode != RealLostContext)
-        destroyContext();
+    destroyContext();
 
     ConsoleDisplayPreference display = (mode == RealLostContext) ? DisplayInConsole: DontDisplayInConsole;
     synthesizeGLError(GC3D_CONTEXT_LOST_WEBGL, "loseContext", "context lost", display);
 
     // Don't allow restoration unless the context lost event has both been
     // dispatched and its default behavior prevented.
     m_restoreAllowed = false;
 
     // Always defer the dispatch of the context lost event, to implement
     // the spec behavior of queueing a task.
@@ skipping 1182 matching lines @@
     if (!frame)
         return;
 
     Settings* settings = frame->settings();
 
     if (!frame->loader().client()->allowWebGL(settings && settings->webGLEnabled()))
         return;
 
     blink::WebGraphicsContext3D::Attributes attributes = m_requestedAttributes->attributes(canvas()->document().topDocument().url().string(), settings);
     OwnPtr<blink::WebGraphicsContext3D> context = adoptPtr(blink::Platform::current()->createOffscreenGraphicsContext3D(attributes));
+
+    if (context) {
+        RefPtr<WebGLRenderingContextEvictionManager> contextEvictionManager = adoptRef(new WebGLRenderingContextEvictionManager());
+
+        // Construct a new drawing buffer with the new WebGraphicsContext3D.
+        m_drawingBuffer->releaseResources();
+        DrawingBuffer::PreserveDrawingBuffer preserve = m_requestedAttributes->preserveDrawingBuffer() ? DrawingBuffer::Preserve : DrawingBuffer::Discard;
+        m_drawingBuffer = DrawingBuffer::create(context.get(), clampedCanvasSize(), preserve, contextEvictionManager.release());
+
+        if (m_drawingBuffer->isZeroSized()) {
+            m_drawingBuffer->releaseResources();
+            context.clear();
+        }
+    }
     if (!context) {
         if (m_contextLostMode == RealLostContext) {
             m_restoreTimer.startOneShot(secondsBetweenRestoreAttempts);
         } else {
             // This likely shouldn't happen but is the best way to report it to the WebGL app.
             synthesizeGLError(GL_INVALID_OPERATION, "", "error restoring context");
         }
         return;
     }
 
-    RefPtr<WebGLRenderingContextEvictionManager> contextEvictionManager = adoptRef(new WebGLRenderingContextEvictionManager());
-
-    // Construct a new drawing buffer with the new WebGraphicsContext3D.
-    m_drawingBuffer->releaseResources();
-    DrawingBuffer::PreserveDrawingBuffer preserve = m_requestedAttributes->preserveDrawingBuffer() ? DrawingBuffer::Preserve : DrawingBuffer::Discard;
-    m_drawingBuffer = DrawingBuffer::create(context.get(), clampedCanvasSize(), preserve, contextEvictionManager.release());
-
-    if (m_drawingBuffer->isZeroSized())
-        return;

[dshwang, 2014/03/10 18:23:31]

Currently, when failing to create fbo, return here. So m_drawingBuffer outlive
with dangling pointer context.get().

-
     m_drawingBuffer->bind();
 
     m_lostContextErrors.clear();
 
     m_context = context.release();
     m_contextLost = false;
 
     setupFlags();
     initializeNewContext();
     canvas()->dispatchEvent(WebGLContextEvent::create(EventTypeNames::webglcontextrestored, false, true, ""));
@@ skipping 186 matching lines @@
         if (m_textureUnits[i].m_texture2DBinding
             || m_textureUnits[i].m_textureCubeMapBinding) {
             m_onePlusMaxNonDefaultTextureUnit = i + 1;
             return;
         }
     }
     m_onePlusMaxNonDefaultTextureUnit = 0;
 }
 
 } // namespace WebCore