GN(Android): Add libosmesa.so to ContentShell.apk

build/toolchain/android/BUILD.gn

Index: build/toolchain/android/BUILD.gn
diff --git a/build/toolchain/android/BUILD.gn b/build/toolchain/android/BUILD.gn
index 313e6090e79ba1fd2c6a73050bd2c9ab04455ea2..66c9a06f16da33016a0a89ffb80d3e240630a857 100644
--- a/build/toolchain/android/BUILD.gn
+++ b/build/toolchain/android/BUILD.gn
@@ -49,6 +49,10 @@ template("android_gcc_toolchain") {
     nm = tool_prefix + "nm"
     strip = "${tool_prefix}strip"
 
+    # Don't use .cr.so for loadable_modules since they are always loaded via
+    # absolute path.
+    loadable_module_extension = ".so"
+
     toolchain_os = "android"
     toolchain_cpu = invoker.toolchain_cpu
   }