Bug 1321387 part 1: Wrap ReflowOutput impl in "namespace mozilla {}". r=TYLin

The class definition (in the header file) is already inside the namespace. But
the method implementations are not (until now), and they've only been compiling
successfully thanks to a "using namespace mozilla" that this file was picking
up from another .cpp file, via unified builds.

MozReview-Commit-ID: ImRBpAVA0en

--HG--
extra : rebase_source : 291e2777187ef9af17e17eecc5e48eb27dd111ec

layout/generic/ReflowOutput.cpp

@@ -36,6 +36,8 @@ nsOverflowAreas::SetAllTo(const nsRect& aRect)
   }
 }
 
+namespace mozilla {
+
 ReflowOutput::ReflowOutput(const ReflowInput& aState,
                                          uint32_t aFlags)
   : mISize(0)
@@ -65,3 +67,5 @@ ReflowOutput::UnionOverflowAreasWithDesiredBounds()
     o.UnionRect(o, rect);
   }
 }
+
+} // namespace mozilla