Factor code to rotate a canvas about a point.

tools/sk_tool_utils.cpp

Index: tools/sk_tool_utils.cpp
diff --git a/tools/sk_tool_utils.cpp b/tools/sk_tool_utils.cpp
index 8303f0979d4407e97b81c2d2e89ef3c66b5c5b18..3d121c41fdf7cfe23b0a0fc2bc91a72cd654edea 100644
--- a/tools/sk_tool_utils.cpp
+++ b/tools/sk_tool_utils.cpp
@@ -23,6 +23,12 @@ DEFINE_bool(portableFonts, false, "Use portable fonts");
 
 namespace sk_tool_utils {
 
+void rotate_about(SkCanvas* canvas, SkScalar degrees, SkScalar px, SkScalar py) {
+    canvas->translate(px, py);
+    canvas->rotate(degrees);
+    canvas->translate(-px, -py);
+}
+
 /* these are the default fonts chosen by Chrome for serif, sans-serif, and monospace */
 static const char* gStandardFontNames[][3] = {
     { "Times", "Helvetica", "Courier" }, // Mac