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/Context.cpp b/src/libANGLE/Context.cpp
index 930f6b6..6da22da 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -3936,8 +3936,8 @@
 
 void Context::attachShader(GLuint program, GLuint shader)
 {
-    auto programObject = mState.mShaderPrograms->getProgram(program);
-    auto shaderObject  = mState.mShaderPrograms->getShader(shader);
+    Program *programObject = mState.mShaderPrograms->getProgram(program);
+    Shader *shaderObject   = mState.mShaderPrograms->getShader(shader);
     ASSERT(programObject && shaderObject);
     programObject->attachShader(shaderObject);
 }