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/tests/DrawTextTest.cpp b/tests/DrawTextTest.cpp
index a98b36f..2f8fe05 100644
--- a/tests/DrawTextTest.cpp
+++ b/tests/DrawTextTest.cpp
@@ -120,11 +120,11 @@
     SkScalar oddballs[] = { 0.0f, (float)INFINITY, (float)NAN, 34359738368.0f };
 
     for (auto x : oddballs) {
-        canvas->drawText("a", 1, +x, 0.0f, SkPaint());
-        canvas->drawText("a", 1, -x, 0.0f, SkPaint());
+        canvas->drawString("a", +x, 0.0f, SkPaint());
+        canvas->drawString("a", -x, 0.0f, SkPaint());
     }
     for (auto y : oddballs) {
-        canvas->drawText("a", 1, 0.0f, +y, SkPaint());
-        canvas->drawText("a", 1, 0.0f, -y, SkPaint());
+        canvas->drawString("a", 0.0f, +y, SkPaint());
+        canvas->drawString("a", 0.0f, -y, SkPaint());
     }
 }