fix skpdiff viewer bug when using relative paths

BUG=skia:1463
R=djsollen@google.com

Review URL: https://codereview.chromium.org/21601002

git-svn-id: http://skia.googlecode.com/svn/trunk@10515 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skpdiff/SkDiffContext.cpp b/tools/skpdiff/SkDiffContext.cpp
index cf2654a..f551ff3 100644
--- a/tools/skpdiff/SkDiffContext.cpp
+++ b/tools/skpdiff/SkDiffContext.cpp
@@ -164,12 +164,15 @@
     while (NULL != currentRecord) {
         stream.writeText("        {\n");
 
+            SkString baselineAbsPath = get_absolute_path(currentRecord->fBaselinePath);
+            SkString testAbsPath = get_absolute_path(currentRecord->fTestPath);
+
             stream.writeText("            \"baselinePath\": \"");
-            stream.writeText(currentRecord->fBaselinePath.c_str());
+            stream.writeText(baselineAbsPath.c_str());
             stream.writeText("\",\n");
 
             stream.writeText("            \"testPath\": \"");
-            stream.writeText(currentRecord->fTestPath.c_str());
+            stream.writeText(testAbsPath.c_str());
             stream.writeText("\",\n");
 
             stream.writeText("            \"diffs\": [\n");