SkPDF: clean up overuse of SK_SUPPORT_PDF

When possible use run-time checks (via SkDocument::CreatePDF)
When PDF is disabled, do not compile tests/PDF*.cpp

Review URL: https://codereview.chromium.org/1278403006
diff --git a/tests/CanvasTest.cpp b/tests/CanvasTest.cpp
index 78253ac..0d5c862 100644
--- a/tests/CanvasTest.cpp
+++ b/tests/CanvasTest.cpp
@@ -570,6 +570,12 @@
     SkAutoTUnref<SkDocument> doc(SkDocument::CreatePDF(&outStream));
 #if SK_SUPPORT_PDF
     REPORTER_ASSERT(reporter, doc);
+#else
+    REPORTER_ASSERT(reporter, !doc);
+#endif  // SK_SUPPORT_PDF
+    if (!doc) {
+        return;
+    }
     SkCanvas* canvas = doc->beginPage(SkIntToScalar(d.fWidth),
                                       SkIntToScalar(d.fHeight));
     REPORTER_ASSERT(reporter, canvas);
@@ -577,9 +583,6 @@
     testStep->draw(canvas, d, reporter);
 
     REPORTER_ASSERT(reporter, doc->close());
-#else
-    REPORTER_ASSERT(reporter, !doc);
-#endif  // SK_SUPPORT_PDF
 }
 
 // The following class groups static functions that need to access