gm: change ErrorBitfield to ErrorType/ErrorCombination

gm/gm_error.h

Index: gm/gm_error.h
===================================================================
--- gm/gm_error.h	(revision 0)
+++ gm/gm_error.h	(revision 0)
@@ -0,0 +1,89 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/*
+ * Error codes used by gmmain.cpp.
+ */
+
+namespace skiagm {
+
+    /**
+     * The complete list of error types we might encounter in GM.
+     */
+    enum ErrorType {
+#if SK_SUPPORT_GPU
+        kNoGpuContext_ErrorType,
+#endif
+        kImageMismatch_ErrorType,
+        kMissingExpectations_ErrorType,
+        kWritingReferenceImage_ErrorType,
+        kLast_ErrorType = kWritingReferenceImage_ErrorType
+    };
+
+    /**
+     * A combination of 0 or more ErrorTypes.
+     */
+    class ErrorCombination {
+    public:
+        ErrorCombination() : fBitfield(0) {}
+        ErrorCombination(const ErrorType type) : fBitfield(1 << type) {}
+
+        /**
+         * Returns true iff there are NO errors.
+         */
+        bool isEmpty() const {
+            return (0 == this->fBitfield);
+        }
+
+        /**
+         * Adds this ErrorType to this ErrorCombination.
+         */
+        void add(const ErrorType type) {
+            this->fBitfield |= (1 << type);
+        }
+
+        /**
+         * Adds all ErrorTypes in "other" to this ErrorCombination.
+         */
+        void add(const ErrorCombination other) {
+            this->fBitfield |= other.fBitfield;
+        }
+
+        /**
+         * Returns true iff this ErrorCombination includes this ErrorType.
+         */
+        bool includes(const ErrorType type) const {
+            return !(0 == (this->fBitfield & (1 << type)));
+        }
+
+        /**
+         * Returns a new ErrorCombination, which includes the union of all
+         * ErrorTypes in two ErrorCombination objects (this and other).
+         */
+        ErrorCombination plus(const ErrorCombination& other) const {
+            ErrorCombination retval;
+            retval.fBitfield = this->fBitfield | other.fBitfield;
+            return retval;
+        }
+
+        /**
+         * Returns a new ErrorCombination, which is a copy of "this"
+         * but with all ErrorTypes in "other" removed.
+         */
+        ErrorCombination minus(const ErrorCombination& other) const {
+            ErrorCombination retval;
+            retval.fBitfield = this->fBitfield & ~(other.fBitfield);
+            return retval;
+        }
+
+    private:
+        int fBitfield;
+    };
+
+    // No errors at all.
+    const static ErrorCombination kEmpty_ErrorCombination;
+}