Add debug property to enable/disable ANGLE

Due to b/118375731 we suspect that loading & unloading the feature
library is causing issues with spurious segfaults or other errors
when starting other apps. Disable use of feature library by default
until issue is resolved.
Bug: 118375731
Test: manual: adb shell setprop debug.angle.enable 1
      Verify that feature library is loaded
      adb shell setprop debug.angle.enable 0
      Verify that feature library is not loaded

Change-Id: I80528acfe5138420085d24c4e7a3fc4e74903b88
diff --git a/opengl/libs/EGL/Loader.cpp b/opengl/libs/EGL/Loader.cpp
index 6f792ec..a7fea33 100644
--- a/opengl/libs/EGL/Loader.cpp
+++ b/opengl/libs/EGL/Loader.cpp
@@ -549,7 +549,14 @@
         char model[PROPERTY_VALUE_MAX];
         property_get("ro.product.manufacturer", manufacturer, "UNSET");
         property_get("ro.product.model", model, "UNSET");
-        so = load_angle_from_namespace("feature_support", ns);
+
+        // Check if ANGLE is enabled. Workaround for b/118375731
+        // We suspect that loading & unloading a library somehow corrupts
+        // the process.
+        property_get("debug.angle.enable", prop, "0");
+        if (atoi(prop)) {
+            so = load_angle_from_namespace("feature_support", ns);
+        }
         if (so) {
             ALOGV("Temporarily loaded ANGLE's opt-in/out logic from namespace");
             bool use_version0_API = false;