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/libANGLE/validationES2.cpp b/src/libANGLE/validationES2.cpp
index cd835b3..5e505aa 100644
--- a/src/libANGLE/validationES2.cpp
+++ b/src/libANGLE/validationES2.cpp
@@ -2533,7 +2533,7 @@
 
 bool ValidateClear(ValidationContext *context, GLbitfield mask)
 {
-    auto fbo = context->getGLState().getDrawFramebuffer();
+    Framebuffer *fbo = context->getGLState().getDrawFramebuffer();
     if (fbo->checkStatus(context) != GL_FRAMEBUFFER_COMPLETE)
     {
         context->handleError(InvalidFramebufferOperation());