Prevent duplicate content script injection defined in manifest.json

chrome/browser/extensions/content_script_apitest.cc

Index: chrome/browser/extensions/content_script_apitest.cc
diff --git a/chrome/browser/extensions/content_script_apitest.cc b/chrome/browser/extensions/content_script_apitest.cc
index c8d442885dff659576a6f2f6fc95385d298d0f84..25de32deca4633ab731a7cd48abd885bc078ed62 100644
--- a/chrome/browser/extensions/content_script_apitest.cc
+++ b/chrome/browser/extensions/content_script_apitest.cc
@@ -335,6 +335,41 @@ class ContentScriptCssInjectionTest : public ExtensionApiTest {
   }
 };
 
+// Test that a script that matches two separate match patterns is only
+// injected once.
+IN_PROC_BROWSER_TEST_F(ExtensionApiTest,
+                       ContentScriptDuplicateScriptInjection) {
+  host_resolver()->AddRule("maps.google.com", "127.0.0.1");
+  ASSERT_TRUE(StartEmbeddedTestServer());
+
+  GURL url = GURL(

[Devlin, 2016/07/19 16:09:00]

nit: no reason for assignment instead of just construction here.  i.e.
GURL url(base::StringPrintf(...))

[catmullings, 2016/07/19 17:10:51]

Done.

+      base::StringPrintf("http://maps.google.com:%i/extensions/test_file.html",
+                         embedded_test_server()->port()));
+
+  ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII(
+      "content_scripts/duplicate_script_injection")));
+
+  ui_test_utils::NavigateToURL(browser(), url);
+
+  bool scripts_injected_once = false;

[Devlin, 2016/07/19 16:09:00]

these variables are somewhat opaque from the test alone, and it's not clear why
we expect 1 vs 2.  I'd suggest adding a few comments to explain what's going on
here so the reader doesn't need to bounce to the content script.

[catmullings, 2016/07/19 17:10:50]

Moved the comment describing the entire TEST_F to the sub-test above and added a
comment for this new sub-test.

Done.

+  ASSERT_TRUE(content::ExecuteScriptAndExtractBool(
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      "window.domAutomationController.send("
+      "document.getElementsByClassName('test-duplicate-script-injection')"
+      ".length == 1)",
+      &scripts_injected_once));
+  ASSERT_TRUE(scripts_injected_once);
+
+  bool scripts_injected_twice = false;
+  ASSERT_TRUE(content::ExecuteScriptAndExtractBool(
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      "window.domAutomationController.send("
+      "document.getElementsByClassName('injected-twice')"
+      ".length == 2)",
+      &scripts_injected_twice));
+  ASSERT_TRUE(scripts_injected_twice);
+}
+
 IN_PROC_BROWSER_TEST_F(ContentScriptCssInjectionTest,
                        ContentScriptInjectsStyles) {
   ASSERT_TRUE(StartEmbeddedTestServer());