Fix the definition of the 'blink_tests' target in build/all.gyp.

The change in #317893 accidentally made the blink_tests target
not exist in an Android build. That was bad :).

TBR=alancutter@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/948323003

Cr-Original-Commit-Position: refs/heads/master@{#317907}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 73638aacdada58d8dab3529c516a4e32c4e07a51

all.gyp

@@ -620,6 +620,10 @@
             }],
           ],
         },
+      ]},
+    ], # OS!="ios" and OS!="android"
+    ['OS!="iOS"', {
+      'targets': [
         {
           'target_name': 'blink_tests',
           'type': 'none',