Apply Chromium style fixes.

This addresses several minor code quality issues that are validated
in Chromium, but not yet applied to ANGLE:

* constructors and destructors must be defined out-of-line
* auto is not allowed for simple pointer types
* use override everywhere instead of virtual
* virtual functions must also be defined out-of-line

Slightly reduces binary size for me (~2k on Win, 150k on Linux).

Bug: angleproject:1569
Change-Id: I073ca3365188caf5f29fb28d9eb207903c1843e6
Reviewed-on: https://chromium-review.googlesource.com/779959
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/compiler/preprocessor/MacroExpander.h b/src/compiler/preprocessor/MacroExpander.h
index 7a4f5a9..fae7676 100644
--- a/src/compiler/preprocessor/MacroExpander.h
+++ b/src/compiler/preprocessor/MacroExpander.h
@@ -52,6 +52,7 @@
     struct MacroContext
     {
         MacroContext();
+        ~MacroContext();
         bool empty() const;
         const Token &get();
         void unget();