Replacing the 'return 0;' statements with 'return nullptr;'

public/platform/WebGraphicsContext3D.h

Index: public/platform/WebGraphicsContext3D.h
diff --git a/public/platform/WebGraphicsContext3D.h b/public/platform/WebGraphicsContext3D.h
index 818f4a63e6da101b6517f503f7528277b020d67e..c210419c8ecf1645eb7fe8d2a56fd4abee4340b1 100644
--- a/public/platform/WebGraphicsContext3D.h
+++ b/public/platform/WebGraphicsContext3D.h
@@ -450,7 +450,7 @@ public:
     virtual void releaseTexImage2DCHROMIUM(WGC3Denum target, WGC3Dint imageId) { }
 
     // GL_CHROMIUM_pixel_transfer_buffer_object
-    virtual void* mapBufferCHROMIUM(WGC3Denum target, WGC3Denum access) { return 0; }
+    virtual void* mapBufferCHROMIUM(WGC3Denum target, WGC3Denum access) { return nullptr; }
     virtual WGC3Dboolean unmapBufferCHROMIUM(WGC3Denum target) { return false; }
 
     // GL_CHROMIUM_async_pixel_transfers
@@ -461,7 +461,7 @@ public:
     // GL_EXT_draw_buffers
     virtual void drawBuffersEXT(WGC3Dsizei n, const WGC3Denum* bufs) { }
 
-    virtual GrGLInterface* createGrGLInterface() { return 0; }
+    virtual GrGLInterface* createGrGLInterface() { return nullptr; }
 
     // GL_CHROMIUM_image
     virtual void destroyImageCHROMIUM(WGC3Duint imageId) { }
@@ -500,7 +500,7 @@ public:
     virtual void deleteTransformFeedback(WebGLId transformfeedback) { }
     virtual void drawRangeElements(WGC3Denum mode, WGC3Duint start, WGC3Duint end, WGC3Dsizei count, WGC3Denum type, WGC3Dintptr offset) { }
     virtual void endTransformFeedback(void) { }
-    virtual WGC3Dsync fenceSync(WGC3Denum condition, WGC3Dbitfield flags) { return 0; }
+    virtual WGC3Dsync fenceSync(WGC3Denum condition, WGC3Dbitfield flags) { return nullptr; }
     virtual void framebufferTextureLayer(WGC3Denum target, WGC3Denum attachment, WGC3Duint texture, WGC3Dint level, WGC3Dint layer) { }
     virtual void getActiveUniformBlockName(WebGLId program, WGC3Duint uniformBlockIndex, WGC3Dsizei bufSize, WGC3Dsizei *length, WGC3Dchar *uniformBlockName) { }
     virtual void getActiveUniformBlockiv(WebGLId program, WGC3Duint uniformBlockIndex, WGC3Denum pname, WGC3Dint *params) { }