Add default rust logo for documentation

Author: GuillaumeGomez

src/librustdoc/html/layout.rs

@@ -177,7 +177,10 @@ pub fn render<T: fmt::Display, S: fmt::Display>(
     root_path = page.root_path,
     css_class = page.css_class,
     logo      = if layout.logo.is_empty() {
-        String::new()
+        format!("<a href='{}{}/index.html'>\
+                 <img src='{static_root_path}rust-logo{suffix}.png' alt='logo' width='100'></a>",
+                static_root_path=static_root_path,
+                suffix=page.resource_suffix)
     } else {
         format!("<a href='{}{}/index.html'>\
                  <img src='{}' alt='logo' width='100'></a>",

src/librustdoc/html/render.rs

@@ -789,6 +789,10 @@ fn write_shared(
         themes.insert(theme.to_owned());
     }
 
+    if (*cx.shared).layout.logo.is_empty() {
+        write(cx.dst.join(&format!("rust-logo{}.png", cx.shared.resource_suffix)),
+              static_files::RUST_LOGO)?;
+    }
     write(cx.dst.join(&format!("brush{}.svg", cx.shared.resource_suffix)),
           static_files::BRUSH_SVG)?;
     write(cx.dst.join(&format!("wheel{}.svg", cx.shared.resource_suffix)),

src/librustdoc/html/static/rust-logo.png

@@ -51,6 +51,9 @@ pub static LICENSE_APACHE: &'static [u8] = include_bytes!("static/LICENSE-APACHE
 /// The contents of `LICENSE-MIT.txt`, the text of the MIT License.
 pub static LICENSE_MIT: &'static [u8] = include_bytes!("static/LICENSE-MIT.txt");
 
+/// The contents of `rust-logo.png`, the default icon of the documentation.
+pub static RUST_LOGO: &'static [u8] = include_bytes!("static/rust-logo.png");
+
 /// The built-in themes given to every documentation site.
 pub mod themes {
     /// The "light" theme, selected by default when no setting is available. Used as the basis for