Cheat to go fast, but be careful in debug mode.

src/core/SkRecordDraw.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRecordDraw.h"
 #include "SkTSort.h"
 
@@ skipping 294 matching lines @@
         for (int i = 1; i < N; i++) {
             left  = SkMinScalar(left,  op.xpos[i]);
             right = SkMaxScalar(right, op.xpos[i]);
         }
         SkRect dst = { left, op.y, right, op.y };
         AdjustTextForFontMetrics(&dst, op.paint);
         return this->adjustAndMap(dst, &op.paint);
     }
 
     static void AdjustTextForFontMetrics(SkRect* rect, const SkPaint& paint) {
-        // FIXME: These bounds should be tight (and correct), but reading SkFontMetrics is likely
-        // a performance bottleneck.  It's safe to overapproximate these metrics for speed.  E.g.
-        // fTop <= 1.5 * paint.getTextSize(), fXMax <= 8 * fTop, etc.
+#if SK_DEBUG
+        SkRect correct = *rect;
+#endif
+        const SkScalar yPad = 1.5f * paint.getTextSize(),  // In practice, this seems to be enough.
+                       xPad = 4.0f * yPad;                 // Hack for very wide Github logo font.
+        rect->outset(xPad, yPad);
+#if SK_DEBUG
         SkPaint::FontMetrics metrics;
         paint.getFontMetrics(&metrics);
-        rect->fLeft   += metrics.fXMin;
-        rect->fTop    += metrics.fTop;
-        rect->fRight  += metrics.fXMax;
-        rect->fBottom += metrics.fBottom;
+        correct.fLeft   += metrics.fXMin;
+        correct.fTop    += metrics.fTop;
+        correct.fRight  += metrics.fXMax;
+        correct.fBottom += metrics.fBottom;
+        SkASSERTF(rect->contains(correct), "%f %f %f %f vs. %f %f %f %f\n",
+                  -xPad, -yPad, +xPad, +yPad,
+                  metrics.fXMin, metrics.fTop, metrics.fXMax, metrics.fBottom);
+#endif
     }
 
     // Returns true if rect was meaningfully adjusted for the effects of paint,
     // false if the paint could affect the rect in unknown ways.
     static bool AdjustForPaint(const SkPaint* paint, SkRect* rect) {
         if (paint) {
             if (paint->canComputeFastBounds()) {
                 *rect = paint->computeFastBounds(*rect, rect);
                 return true;
             }
@@ skipping 45 matching lines @@
     // Used to track the bounds of Save/Restore blocks and the control ops inside them.
     SkTDArray<SaveBounds> fSaveStack;
     SkTDArray<unsigned>   fControlIndices;
 };
 
 }  // namespace SkRecords
 
 void SkRecordFillBounds(const SkRecord& record, SkBBoxHierarchy* bbh) {
     SkRecords::FillBounds(record, bbh);
 }