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 5353 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, 0));
+    RefPtr<DrawingBuffer> drawingBuffer;
+    if (context) {
+        // If the context was lost due to RealLostContext, we need to release FBOs before creating new DrawingBuffer to ensure resource budget enough.
+        m_drawingBuffer->releaseResources();
+        RefPtr<WebGLRenderingContextEvictionManager> contextEvictionManager = adoptRef(new WebGLRenderingContextEvictionManager());
+
+        // Construct a new drawing buffer with the new WebGraphicsContext3D.
+        DrawingBuffer::PreserveDrawingBuffer preserve = m_requestedAttributes->preserveDrawingBuffer() ? DrawingBuffer::Preserve : DrawingBuffer::Discard;
+        drawingBuffer = DrawingBuffer::create(context.get(), clampedCanvasSize(), preserve, contextEvictionManager.release());
+
+        if (drawingBuffer->isZeroSized()) {
+            drawingBuffer.clear();
+            context.clear();
+        }
+    }
     if (!context) {
         if (m_contextLostMode == RealLostContext) {
             m_restoreTimer.startOneShot(secondsBetweenRestoreAttempts, FROM_HERE);
         } 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;
-
+    m_drawingBuffer = drawingBuffer.release();
     m_drawingBuffer->bind();
 
     m_lostContextErrors.clear();
 
     m_context = context.release();
     m_contextLost = false;
 
     setupFlags();
     initializeNewContext();
     markContextChanged(CanvasContextChanged);
@@ skipping 187 matching lines @@
         if (m_textureUnits[i].m_texture2DBinding
             || m_textureUnits[i].m_textureCubeMapBinding) {
             m_onePlusMaxNonDefaultTextureUnit = i + 1;
             return;
         }
     }
     m_onePlusMaxNonDefaultTextureUnit = 0;
 }
 
 } // namespace WebCore