Add factory class for generating various flavors of GrTextContext.

This is the first pass of making Gr*TextContext more generic and easily
subclassed. The next stage will be making GrBitmapTextContext and
GrDistanceFieldTextContext more similar by moving the SkDraw loop into
each subclass.

BUG=skia:2018
R=bsalomon@google.com, reed@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/144283002

git-svn-id: http://skia.googlecode.com/svn/trunk@13142 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrTextContext.cpp b/src/gpu/GrTextContext.cpp
index 9e91628..77e98d2 100644
--- a/src/gpu/GrTextContext.cpp
+++ b/src/gpu/GrTextContext.cpp
@@ -8,7 +8,8 @@
 
 #include "GrTextContext.h"
 
-GrTextContext::GrTextContext(GrContext* context, const GrPaint& paint) : fPaint(paint) {
+GrTextContext::GrTextContext(GrContext* context, const GrPaint& paint,
+                             const SkPaint& skPaint) : fPaint(paint), fSkPaint(skPaint) {
     fContext = context;
 
     const GrClipData* clipData = context->getClip();