Instantiate parameterized PDFExtensionClipboardTest.

https://804113 changed the test to be parameterized, but forgot to
instantiate it. Fix this so the test actually runs.

Bug: 1120279
Change-Id: I7291a1e7e9c857f2295fa0bb23fb1e2995b2f4db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391334Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804373}

chrome/browser/pdf/pdf_extension_test.cc

@@ -2283,6 +2283,10 @@ IN_PROC_BROWSER_TEST_P(PDFExtensionClipboardTest, CombinedShiftArrowPresses) {
   SendCopyCommandAndCheckCopyPasteClipboard("L");
 }
 
+INSTANTIATE_TEST_SUITE_P(/* no prefix */,
+                         PDFExtensionClipboardTest,
+                         testing::Bool());
+
 // Verifies that an <embed> of size zero will still instantiate a guest and post
 // message to the <embed> is correctly forwarded to the extension. This is for
 // catching future regression in docs/ and slides/ pages (see