Fix up -Winconsistent-missing-override

  (and a couple presubmit fixes)

This allows us to turn back on -Werror for LLVM coverage builds,
and more generally supports building with Clang 3.7.

No public API changes.
TBR=reed@google.com

BUG=skia:

Review URL: https://codereview.chromium.org/1232463006
diff --git a/bench/PathBench.cpp b/bench/PathBench.cpp
index 710179a..ffec90b 100644
--- a/bench/PathBench.cpp
+++ b/bench/PathBench.cpp
@@ -148,7 +148,7 @@
     void appendName(SkString* name) override {
         name->append("sawtooth");
     }
-    virtual void makePath(SkPath* path) {
+    void makePath(SkPath* path) override {
         SkScalar x = SkIntToScalar(20);
         SkScalar y = SkIntToScalar(20);
         const SkScalar x0 = x;