rebaseline_server: display as much info as possible if expected/actual image is missing

gm/rebaseline_server/testdata/outputs/expected/compare_to_expectations_test.CompareToExpectationsTest.test_gm/gm.json

 {
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         "Test-Android-GalaxyNexus-SGX540-Arm7-Release": 13, 
         "Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Debug": 15
       }
@@ skipping 31 matching lines @@
         "bigblurs": 7, 
         "bitmapsource": 2, 
         "displacement": 5, 
         "filterbitmap_checkerboard_192_192": 2, 
         "filterbitmap_checkerboard_32_2": 2, 
         "texdata": 1
       }
     }
   }, 
   "header": {
-    "dataHash": "2099241024256114776", 
+    "dataHash": "2775016045957284034", 
     "isEditable": false, 
     "isExported": true, 
     "schemaVersion": 2, 
     "timeNextUpdateAvailable": null, 
     "timeUpdated": 12345678, 
     "type": "all"
   }, 
   "imagePairs": [
     {
       "differenceData": {
@@ skipping 140 matching lines @@
     }, 
     {
       "extraColumns": {
         "builder": "Test-Android-GalaxyNexus-SGX540-Arm7-Release", 
         "config": "565", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/2422083043229439955.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Android-GalaxyNexus-SGX540-Arm7-Release", 
         "config": "8888", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/17309852422285247848.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Android-GalaxyNexus-SGX540-Arm7-Release", 
         "config": "565", 
         "resultType": "no-comparison", 
         "test": "bitmapsource"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bitmapsource/17503582803589749280.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Android-GalaxyNexus-SGX540-Arm7-Release", 
         "config": "8888", 
         "resultType": "no-comparison", 
         "test": "bitmapsource"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bitmapsource/16289727936158057543.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "expectations": {
         "bugs": [
           1578
         ], 
         "ignore-failure": null, 
         "reviewed-by-human": false
       }, 
       "extraColumns": {
@@ skipping 140 matching lines @@
     }, 
     {
       "extraColumns": {
         "builder": "Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Debug", 
         "config": "565", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/14704206703218007573.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Debug", 
         "config": "8888", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/17309852422285247848.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Debug", 
         "config": "gpu", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/1822195599289208664.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Debug", 
         "config": "pdf-mac", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/16171608477794909861.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "extraColumns": {
         "builder": "Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Debug", 
         "config": "pdf-poppler", 
         "resultType": "no-comparison", 
         "test": "bigblurs"
       }, 
       "imageAUrl": null, 
       "imageBUrl": "bitmap-64bitMD5/bigblurs/6539050160610613353.png", 
-      "isDifferent": false
+      "isDifferent": true
     }, 
     {
       "expectations": {
         "bugs": [
           1578
         ], 
         "ignore-failure": null, 
         "reviewed-by-human": false
       }, 
       "extraColumns": {
@@ skipping 91 matching lines @@
     "imageB": {
       "baseUrl": "http://chromium-skia-gm.commondatastorage.googleapis.com/gm", 
       "description": "actual image"
     }, 
     "whiteDiffs": {
       "baseUrl": "/static/generated-images/whitediffs", 
       "description": "differing pixels in white"
     }
   }
 }