Beamer : titres des diapositives avec des dégradés de couleurs

\documentclass{beamer}

\useoutertheme{shadow}
\usepackage{tikz}
\usetikzlibrary{shadings}
\usetikzlibrary{fadings}

\colorlet{titleleft}{yellow!30!white}
\colorlet{titleright}{blue!20!black}

\makeatletter
\pgfdeclarehorizontalshading[titleleft,titleright]
    {beamer@frametitleshade}
  {\paperheight}{%
    color(0pt)=(titleleft);
    color(\paperwidth)=(titleright)
  }

\pgfdeclarehorizontalshading{titlefont}
    {\paperheight}
    {%
        color(0cm)=(titleright); 
        color(0.8cm)=(titleright); 
        color(1.15cm)=(blue);
        color(1.65cm)=(blue!50!cyan);
        color(2cm)=(blue!10!cyan)
    }

% from https://tex.stackexchange.com/questions/45744/how-to-put-color-gradient-to-desired-text-only
\newcommand\shadetext[1]{%
  \begin{tikzfadingfrompicture}[name=tikzsection]
    \node [text=white,inner sep=0pt,outer sep=0pt,text width=.9\linewidth] {#1};
  \end{tikzfadingfrompicture}%
  \begin{tikzpicture}%
    \node [text=white,inner sep=0pt,outer sep=0pt,text width=.9\linewidth,opacity=0] (textnode) {#1};
    \shade[path fading=tikzsection,fit fading=false,shading=titlefont,text width=.9\linewidth,inner sep=0pt,outer sep=0pt]
    (textnode.south west) rectangle (textnode.north east);
  \end{tikzpicture}%
}

\setbeamertemplate{frametitle}{%
  \nointerlineskip%
  \vskip-2pt%
  \hbox{\leavevmode
    \advance\beamer@leftmargin by -12bp%
    \advance\beamer@rightmargin by -12bp%
    \beamer@tempdim=\textwidth%
    \advance\beamer@tempdim by \beamer@leftmargin%
    \advance\beamer@tempdim by \beamer@rightmargin%
    \hskip-\Gm@lmargin\hbox{%
      \setbox\beamer@tempbox=\hbox{\begin{minipage}[b]{\paperwidth}%
          \vbox{}
          \vskip-0.0ex%
          \leftskip0.3cm%
          \rightskip0.3cm plus1fil\leavevmode
          \usebeamercolor[fg]{frametitle}\shadetext{\usebeamerfont{frametitle}\strut\insertframetitle\strut}\par%
          \ifx\insertframesubtitle\@empty\else%
            {\usebeamerfont*{framesubtitle}{\usebeamercolor[fg]{framesubtitle}\insertframesubtitle}\strut\par}%
          \fi%
          \nointerlineskip
          \vbox{}%
          \end{minipage}}%
      \beamer@tempdim=\ht\beamer@tempbox%
      \advance\beamer@tempdim by 4pt%
      \begin{pgfpicture}{0pt}{0pt}{\paperwidth}{\beamer@tempdim}
        \usebeamercolor{frametitle right}
        \pgfpathrectangle{\pgfpointorigin}{\pgfpoint{\paperwidth}{\beamer@tempdim}}
        \pgfusepath{clip}
        \pgftext[left,base]{\pgfuseshading{beamer@frametitleshade}}
      \end{pgfpicture}
      \hskip-\paperwidth%
      \box\beamer@tempbox%
    }%
    \hskip-\Gm@rmargin%
  }%
  \nointerlineskip
    \vskip-0.2pt
    \hbox to\textwidth{\hskip-\Gm@lmargin\pgfuseshading{beamer@topshade}\hskip-\Gm@rmargin}
    \vskip-2pt
}
\makeatother

\begin{document}

\begin{frame}
\frametitle{Very very long frame title reaching the end of the line and continuing in the next line}
\end{frame}

\end{document}