Oilpan: disable conservative GCs during initial GC mixin construction.

Source/core/html/canvas/WebGL2RenderingContextBase.h

 // Copyright 2015 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.
 
 #ifndef WebGL2RenderingContextBase_h
 #define WebGL2RenderingContextBase_h
 
 #include "core/html/canvas/WebGLExtension.h"
 #include "core/html/canvas/WebGLRenderingContextBase.h"
 #include "wtf/PassRefPtr.h"
 
 namespace blink {
 
 class WebGLTexture;
 
 class WebGLActiveInfo;
 class WebGLBuffer;
 class WebGLProgram;
 class WebGLQuery;
 class WebGLSampler;
 class WebGLSync;
 class WebGLTransformFeedback;
 class WebGLUniformLocation;
 class WebGLVertexArrayObject;
 
 class WebGL2RenderingContextBase : public WebGLRenderingContextBase {
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(WebGL2RenderingContextBase);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN_NESTED(WebGL2RenderingContextBase, WebGLRenderingContextBase);
 public:
     virtual ~WebGL2RenderingContextBase();
 
     /* Buffer objects */
     void copyBufferSubData(GLenum, GLenum, GLintptr, GLintptr, GLsizeiptr);
     void getBufferSubData(GLenum target, GLintptr offset, DOMArrayBuffer* returnedData);
 
     /* Framebuffer objects */
     void blitFramebuffer(GLint, GLint, GLint, GLint, GLint, GLint, GLint, GLint, GLbitfield, GLenum);
     void framebufferTextureLayer(GLenum, GLenum, const WebGLTexture*, GLint, GLint);
@@ skipping 133 matching lines @@
     bool validateAndUpdateBufferBindTarget(const char* functionName, GLenum, WebGLBuffer*) override;
 };
 
 DEFINE_TYPE_CASTS(WebGL2RenderingContextBase, CanvasRenderingContext, context,
     context->is3d() && WebGLRenderingContextBase::getWebGLVersion(context) >= 2,
     context.is3d() && WebGLRenderingContextBase::getWebGLVersion(&context) >= 2);
 
 } // namespace blink
 
 #endif