Add appendPrecisionModifier method to GrGLSLShaderBuilder

src/gpu/glsl/GrGLSLShaderBuilder.h

Index: src/gpu/glsl/GrGLSLShaderBuilder.h
diff --git a/src/gpu/glsl/GrGLSLShaderBuilder.h b/src/gpu/glsl/GrGLSLShaderBuilder.h
index 5b3a01f3e923a9918e76e82b263f9cab7f88b338..cddf7b2db429ca18643a37e03fc85ee99edd37c6 100644
--- a/src/gpu/glsl/GrGLSLShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLShaderBuilder.h
@@ -93,6 +93,11 @@ public:
      */
     void declAppend(const GrGLSLShaderVar& var);
 
+    /**
+     * Appends a precision qualifier followed by a space, if relevant for the GLSL version.
+     */
+    void appendPrecisionModifier(GrSLPrecision);
+
     /** Emits a helper function outside of main() in the fragment shader. */
     void emitFunction(GrSLType returnType,
                       const char* name,