Bug 1321387 part 2: Add missing "using namespace" declarations to a few .cpp files in layout/generic. r=TYLin

This adds 2 "using namespace mozilla" (to provide various types),
and 2 "using namespace mozilla::gfx" (to provide mozilla::gfx::DrawTarget).

MozReview-Commit-ID: 2bXbMlr4Dbn

layout/generic/nsRubyBaseContainerFrame.cpp

@@ -22,6 +22,7 @@
 #include "RubyUtils.h"
 
 using namespace mozilla;
+using namespace mozilla::gfx;
 
 //----------------------------------------------------------------------