Revert of webgl: use immutable texture for the default FBO.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 51 matching lines @@
 class WebLayer;
 
 // Manages a rendering target (framebuffer + attachment) for a canvas.  Can publish its rendering
 // results to a WebLayer for compositing.
 class PLATFORM_EXPORT DrawingBuffer : public RefCounted<DrawingBuffer>, public WebExternalTextureLayerClient  {
     // If we used CHROMIUM_image as the backing storage for our buffers,
     // we need to know the mapping from texture id to image.
     struct TextureInfo {
         Platform3DObject textureId;
         WGC3Duint imageId;
-        bool immutable;
 
         TextureInfo()
             : textureId(0)
             , imageId(0)
-            , immutable(false)
         {
         }
     };
 
     struct MailboxInfo : public RefCounted<MailboxInfo> {
         WebExternalTextureMailbox mailbox;
         TextureInfo textureInfo;
         IntSize size;
         // This keeps the parent drawing buffer alive as long as the compositor is
         // referring to one of the mailboxes DrawingBuffer produced. The parent drawing buffer is
@@ skipping 137 matching lines @@
         ReadbackSkia
     };
 
     // Helper function which does a readback from the currently-bound
     // framebuffer into a buffer of a certain size with 4-byte pixels.
     void readBackFramebuffer(unsigned char* pixels, int width, int height, ReadbackOrder, WebGLImageConversion::AlphaOp);
 
     // Helper function to flip a bitmap vertically.
     void flipVertically(uint8_t* data, int width, int height);
 
+    // Helper to texImage2D with pixel==0 case: pixels are initialized to 0.
+    // By default, alignment is 4, the OpenGL default setting.
+    void texImage2DResourceSafe(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, GLint alignment = 4);
     // Allocate buffer storage to be sent to compositor using either texImage2D or CHROMIUM_image based on available support.
     void allocateTextureMemory(TextureInfo*, const IntSize&);
     void deleteChromiumImageForTexture(TextureInfo*);
 
     PreserveDrawingBuffer m_preserveDrawingBuffer;
     bool m_scissorEnabled;
     Platform3DObject m_texture2DBinding;
     Platform3DObject m_drawFramebufferBinding;
     Platform3DObject m_readFramebufferBinding;
     GLenum m_activeTextureUnit;
 
     OwnPtr<WebGraphicsContext3D> m_context;
     OwnPtr<Extensions3DUtil> m_extensionsUtil;
     IntSize m_size;
     WebGraphicsContext3D::Attributes m_requestedAttributes;
     bool m_multisampleExtensionSupported;
     bool m_packedDepthStencilExtensionSupported;
     bool m_discardFramebufferSupported;
-    bool m_storageTextureSupported;
     Platform3DObject m_fbo;
     // DrawingBuffer's output is double-buffered. m_colorBuffer is the back buffer.
     TextureInfo m_colorBuffer;
     struct FrontBufferInfo {
         TextureInfo texInfo;
         WebExternalTextureMailbox mailbox;
     };
     FrontBufferInfo m_frontColorBuffer;
 
     // This is used when we have OES_packed_depth_stencil.
@@ skipping 48 matching lines @@
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace blink
 
 #endif // DrawingBuffer_h