Add an extension for querying esimated GPU memory size of resources.

BUG=892288

Change-Id: I56fc3ab00c06d711e1a21eb1ad4b2224126730dc
Reviewed-on: https://chromium-review.googlesource.com/c/1262021
Reviewed-by: Yuly Novikov <ynovikov@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index bafb7fb..fbcd3f0 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -3243,6 +3243,8 @@
         supportedExtensions.explicitContext = true;
     }
 
+    supportedExtensions.memorySize = true;
+
     return supportedExtensions;
 }