Modify skpdiff to write diffs directly to provided directories

tools/skpdiff/SkDiffContext.h

Index: tools/skpdiff/SkDiffContext.h
diff --git a/tools/skpdiff/SkDiffContext.h b/tools/skpdiff/SkDiffContext.h
index 996737f2eed6e3ac1ce89411c8fde4b4e9e4aa02..793c5028ce51edd836559638f7f432471ba75bdb 100644
--- a/tools/skpdiff/SkDiffContext.h
+++ b/tools/skpdiff/SkDiffContext.h
@@ -52,6 +52,15 @@ public:
     void setWhiteDiffDir(const SkString& directory);
 
     /**
+     * Sets a flag wether to generate file names that a combination 
+     * of the baseline and test input files. 
+     * 
+     * If false the output file names are the common prefix of the 
+     * two inputs. 
+     */
+    void setLongNames(const bool useLongNames);
+
+    /**
      * Sets the differs to be used in each diff. Already started diffs will not retroactively use
      * these.
      * @param differs An array of differs to use. The array is copied, but not the differs
@@ -177,6 +186,7 @@ private:
     SkString fAlphaMaskDir;
     SkString fRgbDiffDir;
     SkString fWhiteDiffDir;
+    bool longNames;
 };
 
 #endif