Bug 1424673 - Fix the clip region for text draw target. r=kats

For draw target, the initial clip region should be the draw target's size.

MozReview-Commit-ID: 2z2EobkYFs2

--HG--
extra : rebase_source : 9631cf189330b089992b8458113800ea9a3fd4a0

layout/generic/TextDrawTarget.h

@@ -63,14 +63,11 @@ public:
     LayoutDeviceRect layoutBoundsRect = LayoutDeviceRect::FromAppUnits(
         aBounds, appUnitsPerDevPixel);
     LayoutDeviceRect layoutClipRect = layoutBoundsRect;
-
-    auto clip = aItem->GetClip();
-    if (clip.HasClip()) {
-      layoutClipRect = LayoutDeviceRect::FromAppUnits(
-                  clip.GetClipRect(), appUnitsPerDevPixel);
-    }
-
     mBoundsRect = aSc.ToRelativeLayoutRect(layoutBoundsRect);
+
+    // Add 1 pixel of dirty area around clip rect to allow us to paint
+    // antialiased pixels beyond the measured text extents.
+    layoutClipRect.Inflate(1);
     mClipRect = aSc.ToRelativeLayoutRect(layoutClipRect);
 
     mBackfaceVisible = !aItem->BackfaceIsHidden();