Add unittest for showing spelling panel on mac via EditCommand

Repurpose spell checking code that was testing for the mojo channel
to common code. Write a test that causes the showGuessPanel selector
to be sent and verify the panel is requested to be shown.

BUG=782836

Change-Id: I9d8ac59ac3bf96bbcd7e538f794eac71e0bc7553
Reviewed-on: https://chromium-review.googlesource.com/786260
Commit-Queue: Dave Tapuska <[email protected]>
Reviewed-by: Rachel Blum <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Cr-Commit-Position: refs/heads/master@{#522088}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 9835649..5d221355 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -4762,6 +4762,15 @@
       "extensions/fake_safe_browsing_database_manager.h",
     ]
   }
+
+  if (has_spellcheck_panel) {
+    sources += [
+      "spellchecker/test/spellcheck_content_browser_client.cc",
+      "spellchecker/test/spellcheck_content_browser_client.h",
+      "spellchecker/test/spellcheck_mock_panel_host.cc",
+      "spellchecker/test/spellcheck_mock_panel_host.h",
+    ]
+  }
 }
 
 static_library("test_support_ui") {