add drawString helper to canvas

Many tests and examples use drawText with
a guess of how long the text is in bytes,
or a call to strlen(). Add a helper to
SkCanvas to simplify these examples.

Add another helper for SkString.

R=reed@google.com

Change-Id: I0204a31e938f065606f08ee7cd9a6b36db791ee2
Reviewed-on: https://skia-review.googlesource.com/13642
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Cary Clark <caryclark@skia.org>
diff --git a/gm/stroketext.cpp b/gm/stroketext.cpp
index f1bb327..ec939d1 100644
--- a/gm/stroketext.cpp
+++ b/gm/stroketext.cpp
@@ -31,7 +31,7 @@
 
     if (strokeWidth > 0) {
         p.setStyle(SkPaint::kFill_Style);
-        canvas->drawText("P", 1, loc.fX, loc.fY - 225, p);
+        canvas->drawString("P", loc.fX, loc.fY - 225, p);
         canvas->drawPosText("P", 1, &loc, p);
     }
 
@@ -39,7 +39,7 @@
     p.setStyle(SkPaint::kStroke_Style);
     p.setStrokeWidth(strokeWidth);
 
-    canvas->drawText("P", 1, loc.fX, loc.fY - 225, p);
+    canvas->drawString("P", loc.fX, loc.fY - 225, p);
     canvas->drawPosText("P", 1, &loc, p);
 }