Make GrGLEffects use an interface to append their code.

A small step towards encapsulating GrGLShaderBuilder.
Review URL: https://codereview.chromium.org/12547012

git-svn-id: http://skia.googlecode.com/svn/trunk@8018 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkString.cpp b/src/core/SkString.cpp
index 5d1b8ce..3f9a99f 100644
--- a/src/core/SkString.cpp
+++ b/src/core/SkString.cpp
@@ -531,6 +531,13 @@
     this->append(buffer, strlen(buffer));
 }
 
+void SkString::appendf(const char format[], va_list args) {
+    char    buffer[kBufferSize];
+    VSNPRINTF(buffer, kBufferSize, format, args);
+
+    this->append(buffer, strlen(buffer));
+}
+
 void SkString::prependf(const char format[], ...) {
     char    buffer[kBufferSize];
     ARGS_TO_BUFFER(format, buffer, kBufferSize);