Refactor some entry point stuff.

BUG=angleproject:747

Change-Id: I80634b5e6de8bae1433c49a56a92d3b19c24e11d
Reviewed-on: https://chromium-review.googlesource.com/395568
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/ResourceManager.cpp b/src/libANGLE/ResourceManager.cpp
index 713c104..d3dc102 100644
--- a/src/libANGLE/ResourceManager.cpp
+++ b/src/libANGLE/ResourceManager.cpp
@@ -309,7 +309,7 @@
     }
 }
 
-Shader *ResourceManager::getShader(unsigned int handle)
+Shader *ResourceManager::getShader(unsigned int handle) const
 {
     auto shader = mShaderMap.find(handle);