Move the user agent styles sheets to blink_resources.grd (Part 2) with Unit test support

Blink should make use of blink_resources.grd for the inline resources of user agent stylesheets.
This removes the dependency upon using make-file-arrays.py which embeds these resources as strings.

This patch adds the necessary plumbing required for the webkit_unit_tests target.
As the resources are being moved into blink_resources.grd, this generates blink_resources.pak.
This pak doesn't exists as a separate pak file but its repacked into "content_shell.pak".
The same must be loaded into the data_pack_ of the TestContentClient so that the webkit (blink) unit
tests run successfully.

Part 1: https://codereview.chromium.org/436843004/
Part 1 with conditional: https://codereview.chromium.org/440683004/
Part 2: https://codereview.chromium.org/422023008
Part 3: https://codereview.chromium.org/438843004/

BUG=312586

Review URL: https://codereview.chromium.org/456413002

Cr-Commit-Position: refs/heads/master@{#294554}
diff --git a/content/content_unittests.isolate b/content/content_unittests.isolate
index 98f26ed..ae821ba 100644
--- a/content/content_unittests.isolate
+++ b/content/content_unittests.isolate
@@ -11,10 +11,17 @@
         ],
       },
     }],
-    ['OS=="android" or OS=="mac" or OS=="win"', {
+    ['OS=="android"', {
       'variables': {
         'isolate_dependency_tracked': [
-          '<(PRODUCT_DIR)/content_resources.pak',
+          '<(PRODUCT_DIR)/content_shell/assets/content_shell.pak',
+        ],
+      },
+    }],
+    ['OS=="mac" or OS=="win"', {
+      'variables': {
+        'isolate_dependency_tracked': [
+          '<(PRODUCT_DIR)/content_shell.pak',
         ],
       },
     }],