Fix a crash from letting a local variable rely on a value from a reference-counted font-metrics object that could die, leaving that local variable with an outdated value, b=213390, r+sr=roc, a=asa

gfx/src/windows/nsRenderingContextWin.cpp

@@ -216,7 +216,7 @@ nsRenderingContextWin :: nsRenderingContextWin()
   mOrigFont = NULL;
   mOrigSolidPen = NULL;
   mCurrBrushColor = RGB(255, 255, 255);
-  mCurrFontMetrics = nsnull;
+  mCurrFontWin = nsnull;
   mCurrPenColor = NULL;
   mCurrPen = NULL;
   mNullPen = NULL;
@@ -983,6 +983,7 @@ NS_IMETHODIMP nsRenderingContextWin :: GetLineStyle(nsLineStyle &aLineStyle)
 
 NS_IMETHODIMP nsRenderingContextWin :: SetFont(const nsFont& aFont, nsIAtom* aLangGroup)
 {
+  mCurrFontWin = nsnull; // owned & released by mFontMetrics
   NS_IF_RELEASE(mFontMetrics);
   mContext->GetMetricsFor(aFont, aLangGroup, mFontMetrics);
 
@@ -991,6 +992,7 @@ NS_IMETHODIMP nsRenderingContextWin :: SetFont(const nsFont& aFont, nsIAtom* aLa
 
 NS_IMETHODIMP nsRenderingContextWin :: SetFont(nsIFontMetrics *aFontMetrics)
 {
+  mCurrFontWin = nsnull; // owned & released by mFontMetrics
   NS_IF_RELEASE(mFontMetrics);
   mFontMetrics = aFontMetrics;
   NS_IF_ADDREF(mFontMetrics);
@@ -2641,9 +2643,7 @@ HBRUSH nsRenderingContextWin :: SetupSolidBrush(void)
 
 void nsRenderingContextWin :: SetupFontAndColor(void)
 {
-  if (((mFontMetrics != mCurrFontMetrics) || (NULL == mCurrFontMetrics)) &&
-      (nsnull != mFontMetrics))
-  {
+  if (mFontMetrics && (!mCurrFontWin || mCurrFontWin->mFont != mCurrFont)) {
     nsFontHandle  fontHandle;
     mFontMetrics->GetFontHandle(fontHandle);
     HFONT         tfont = (HFONT)fontHandle;
@@ -2657,8 +2657,6 @@ void nsRenderingContextWin :: SetupFontAndColor(void)
     // When making changes in the font code, set |useAFunctions = 1| in nsGfxFactoryWin
     // to verify that the changes didn't let the 'A' versions out of sync. 
     NS_ASSERTION(mCurrFontWin, "internal error");
-
-    mCurrFontMetrics = mFontMetrics;
   }
 
   if (mCurrentColor != mCurrTextColor)

gfx/src/windows/nsRenderingContextWin.h

@@ -228,6 +228,7 @@ friend class nsNativeThemeWin;
 
 protected:
   nscolor            mCurrentColor;
+  // current font-metrics set in this RC
   nsIFontMetrics    *mFontMetrics;
   HDC               mDC;
   HDC               mMainDC;
@@ -249,7 +250,10 @@ protected:
   nsVoidArray       *mStateCache;
   nscolor           mCurrBrushColor;
   HBRUSH            mCurrBrush;
-  nsIFontMetrics    *mCurrFontMetrics;
+  // mFontMetrics owns mCurrFontWin which is a thin wrapper
+  // around mCurrFont (the actual GDI font handle). These variables
+  // allow us to quickly tell the current selected font and to
+  // avoid the extra cost of a redundant setup of the same font.
   nsFontWin         *mCurrFontWin;
   HFONT             mCurrFont;
   nscolor           mCurrPenColor;