Prevent duplicate content script injection defined in manifest.json (reland)

chrome/test/data/extensions/api_test/content_scripts/duplicate_script_injection/manifest.json

Index: chrome/test/data/extensions/api_test/content_scripts/duplicate_script_injection/manifest.json
diff --git a/chrome/test/data/extensions/api_test/content_scripts/duplicate_script_injection/manifest.json b/chrome/test/data/extensions/api_test/content_scripts/duplicate_script_injection/manifest.json
new file mode 100644
index 0000000000000000000000000000000000000000..7ee939ef456876476027f02091a4c226b7c4da0f
--- /dev/null
+++ b/chrome/test/data/extensions/api_test/content_scripts/duplicate_script_injection/manifest.json
@@ -0,0 +1,29 @@
+{
+  "name": "duplicate script injection",
+  "version": "0.0.1",
+  "manifest_version": 2,
+  "description": "Tests that content scripts assigned to two overlapping url matches are not injected twice. Note this can be extended to N matches",
+  "background": {},
+  "content_scripts": [
+    {
+      "matches": ["*://*.google.com/*"],
+      "js": ["should_run_once.js"],
+      "run_at": "document_end"
+    },
+    {
+      "matches": ["*://maps.google.com/*"],
+      "js": ["should_run_once.js", "should_run_twice.js"],
+      "run_at": "document_end"
+    },
+    {
+      "matches": ["*://maps.google.com/*"],
+      "js": ["should_run_twice.js"],
+      "run_at": "document_idle"
+    },
+    {
+      "matches": ["*://*.maps.google.com/*"],

[Devlin, 2016/08/22 22:46:52]

I don't think this would be sufficient to replicate the crash, because
*.maps.google.com won't match maps.google.com.

[catmullings, 2016/08/24 01:13:19]

It turns out that *.maps.google.com does match maps.google.com; I had tested it
it out just to make sure. I can show you the test, if you'd like.

Also in theory, it should match, according to the third example pattern on the
match pattern documentation
(https://developer.chrome.com/extensions/match_patterns).

[Devlin, 2016/08/25 16:52:25]

Ah, right you are!  Thanks for correcting me.

+      "js": ["should_run_once.js"],
+      "run_at": "document_end"
+    }
+  ]
+}