Fix "error: expected expression" in hosted_app_browsertest.

This commit fixes the "error: expected expression." error.
It looks like ICECC+Clang resolves the " wrongly and, thus,
fails to compile.

The warning before the actual error is
"warning: missing terminating '"' character". It also shows
how the R script portion is resolved, and shows missing ".

Bug: 
Change-Id: Ia4eac8ce8cb47c6b0163ce5f4043dd2be960d6f8
Reviewed-on: https://chromium-review.googlesource.com/822436Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#523839}

chrome/browser/ui/extensions/hosted_app_browsertest.cc

@@ -727,11 +727,11 @@ IN_PROC_BROWSER_TEST_P(HostedAppProcessModelTest, IframesInsideHostedApp) {
   // Verify that |same_dir| and |diff_dir| can script each other.
   // (they should - they have the same origin).
   std::string inner_text_from_other_frame;
-  ASSERT_TRUE(content::ExecuteScriptAndExtractString(
-      diff_dir,
+  const std::string r_script =
       R"( var w = window.open('', 'SameOrigin-SamePath');
-          domAutomationController.send(w.document.body.innerText); )",
-      &inner_text_from_other_frame));
+          domAutomationController.send(w.document.body.innerText); )";
+  ASSERT_TRUE(content::ExecuteScriptAndExtractString(
+      diff_dir, r_script, &inner_text_from_other_frame));
   EXPECT_EQ("Simple test page.", inner_text_from_other_frame);
 }