rebaseline.py: fix --add-new when there are no expectations at all

tools/tests/rebaseline/output/add-new/output-expected/gm-expectations/Test-Android-GalaxyNexus-SGX540-Arm7-Debug/expected-results.json

Index: tools/tests/rebaseline/output/add-new/output-expected/gm-expectations/Test-Android-GalaxyNexus-SGX540-Arm7-Debug/expected-results.json
===================================================================
--- tools/tests/rebaseline/output/add-new/output-expected/gm-expectations/Test-Android-GalaxyNexus-SGX540-Arm7-Debug/expected-results.json	(revision 0)
+++ tools/tests/rebaseline/output/add-new/output-expected/gm-expectations/Test-Android-GalaxyNexus-SGX540-Arm7-Debug/expected-results.json	(working copy)
@@ -1,11 +1,21 @@
 {
   "expected-results": {
     "3x3bitmaprect_565.png": {
-      "allowed-digests": null, 
+      "allowed-digests": [
+        [
+          "bitmap-64bitMD5", 

[epoger, 2013/09/03 15:53:10]

Patchset 4: now that --add-new is being used, the actual checksums from the
"no-comparison" part of this platform's actual-results.json are being filled in
here, as expected.

+          16998423976396106083
+        ]
+      ], 
       "ignore-failure": false
     }, 
     "3x3bitmaprect_8888.png": {
-      "allowed-digests": null, 
+      "allowed-digests": [
+        [
+          "bitmap-64bitMD5", 
+          2054956815327187963
+        ]
+      ], 
       "ignore-failure": false
     }, 
     "aaclip_gpu.png": {
@@ -56,7 +66,12 @@
       "ignore-failure": false
     }, 
     "xfermodeimagefilter_pdf.png": {
-      "allowed-digests": null, 
+      "allowed-digests": [
+        [
+          "bitmap-64bitMD5", 
+          16502178848783208088
+        ]
+      ], 
       "ignore-failure": false
     }, 
     "xfermodes_pdf.png": {