Added code to nsFontMetricsGTK to cache the width of a single space.

Modifed nsRenderingContextGTK::GetWidth to detect when a single space
is passed in and pass back the cached value, rather than re-measuring
a space.

gfx/src/gtk/nsFontMetricsGTK.cpp

@@ -60,6 +60,7 @@ nsFontMetricsGTK::nsFontMetricsGTK()
   mStrikeoutOffset = 0;
   mUnderlineSize = 0;
   mUnderlineOffset = 0;
+  mSpaceWidth = 0;
 }
 
 nsFontMetricsGTK::~nsFontMetricsGTK()
@@ -418,6 +419,9 @@ void nsFontMetricsGTK::RealizeFont()
   // 56% of ascent, best guess for non-true type
   mXHeight = NSToCoordRound((float) fontInfo->ascent* f * 0.56f);
 
+  gint rawWidth = gdk_text_width(mFontHandle, " ", 1); 
+  mSpaceWidth = NSToCoordRound(rawWidth * f);
+
   unsigned long pr = 0;
 
   if (::XGetFontProperty(fontInfo, XA_X_HEIGHT, &pr))
@@ -2179,4 +2183,11 @@ nsFontMetricsGTK::DrawString(nsDrawingSurfaceGTK* aSurface, nsFontGTK* aFont,
     aY + aFont->mBaselineAdjust, (char*) buf, len);
 }
 
+nsresult
+nsFontMetricsGTK::GetSpaceWidth(nscoord &aSpaceWidth)
+{
+  aSpaceWidth = mSpaceWidth;
+  return NS_OK;
+}
+
 #endif /* FONT_SWITCHING */

gfx/src/gtk/nsFontMetricsGTK.h

@@ -99,6 +99,8 @@ public:
   NS_IMETHOD  GetMaxAdvance(nscoord &aAdvance);
   NS_IMETHOD  GetFont(const nsFont *&aFont);
   NS_IMETHOD  GetFontHandle(nsFontHandle &aHandle);
+  
+  virtual nsresult GetSpaceWidth(nscoord &aSpaceWidth);
 
 #ifdef FONT_SWITCHING
 
@@ -149,6 +151,7 @@ protected:
   nscoord             mStrikeoutOffset;
   nscoord             mUnderlineSize;
   nscoord             mUnderlineOffset;
+  nscoord             mSpaceWidth;
 
 #ifdef FONT_SWITCHING
 

gfx/src/gtk/nsRenderingContextGTK.cpp

@@ -913,6 +913,12 @@ NS_IMETHODIMP nsRenderingContextGTK::FillArc(nscoord aX, nscoord aY,
 NS_IMETHODIMP
 nsRenderingContextGTK::GetWidth(char aC, nscoord &aWidth)
 {
+    // Check for the very common case of trying to get the width of a single
+    // space.
+  if ((aC == ' ') && (nsnull != mFontMetrics)) {
+    nsFontMetricsGTK* fontMetricsGTK = (nsFontMetricsGTK*)mFontMetrics;
+    return fontMetricsGTK->GetSpaceWidth(aWidth);
+  }
   return GetWidth(&aC, 1, aWidth);
 }