Added mangleString member and  onBefore*, onAfter* functions to GrGLFragmentShaderBuilder

BUILDS! Added mangleString, onBefore, and onAfterChildProcEmitCode() to GrGLFragmentShaderBuilder.cpp

BUG=skia:4182

Review URL: https://codereview.chromium.org/1288723002
diff --git a/src/gpu/GrProcessor.cpp b/src/gpu/GrProcessor.cpp
index 6cc2a20..39c55a6 100644
--- a/src/gpu/GrProcessor.cpp
+++ b/src/gpu/GrProcessor.cpp
@@ -150,8 +150,9 @@
     int index = fChildProcessors.count();
     fChildProcessors.push_back(GrFragmentStage(child));
 
-    if (child->willReadFragmentPosition())
+    if (child->willReadFragmentPosition()) {
         this->setWillReadFragmentPosition();
+    }
 
     return index;
 }