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/renderer/TextureImpl.cpp b/src/libANGLE/renderer/TextureImpl.cpp
index 34480d8..830d30e 100644
--- a/src/libANGLE/renderer/TextureImpl.cpp
+++ b/src/libANGLE/renderer/TextureImpl.cpp
@@ -19,6 +19,11 @@
 {
 }
 
+gl::Error TextureImpl::onDestroy(const gl::Context *context)
+{
+    return gl::NoError();
+}
+
 gl::Error TextureImpl::copyTexture(const gl::Context *context,
                                    GLenum target,
                                    size_t level,