Do not try to get a display name from an input method ID which starts with "_ext_ime".

chrome/browser/chromeos/input_method/input_method_util_unittest.cc

Index: chrome/browser/chromeos/input_method/input_method_util_unittest.cc
diff --git a/chrome/browser/chromeos/input_method/input_method_util_unittest.cc b/chrome/browser/chromeos/input_method/input_method_util_unittest.cc
index aae6745568b87603af367ca558eb8da50642de0a..91bf4f49fc27866e8803ccad6e944ba0003ab721 100644
--- a/chrome/browser/chromeos/input_method/input_method_util_unittest.cc
+++ b/chrome/browser/chromeos/input_method/input_method_util_unittest.cc
@@ -30,6 +30,9 @@
 #endif  // USE_VIRTUAL_KEYBOARD
 
 namespace chromeos {
+
+extern const char* kExtensionImePrefix;
+
 namespace input_method {
 
 namespace {
@@ -193,6 +196,13 @@ TEST_F(InputMethodUtilTest, TestIsKeyboardLayout) {
   EXPECT_FALSE(InputMethodUtil::IsKeyboardLayout("mozc"));
 }
 
+TEST_F(InputMethodUtilTest, TestExtensionInputMethod) {
+  EXPECT_TRUE(InputMethodUtil::IsExtensionInputMethod(
+      kExtensionImePrefix + std::string("123abc")));
+  EXPECT_FALSE(InputMethodUtil::IsExtensionInputMethod(""));
+  EXPECT_FALSE(InputMethodUtil::IsExtensionInputMethod("mozc"));
+}
+
 TEST_F(InputMethodUtilTest, TestGetKeyboardLayoutName) {
   // Unsupported case.
   EXPECT_EQ("", util_.GetKeyboardLayoutName("UNSUPPORTED_ID"));