[Logging] Implement log levels

Implement suppression of logging below specific levels,
for WTD-793.

platform/framework/src/LogLevel.js

@@ -5,8 +5,72 @@ define(
     function () {
         "use strict";
 
-        function LogLevel() {
+        // Log levels; note that these must be in order of
+        // most-important-first for LogLevel to function correctly
+        // as implemented.
+        var LOG_LEVELS = [
+            'error',
+            'warn',
+            'info',
+            'log',
+            'debug'
+        ];
 
+        // No-op, to replace undesired log levels with
+        function NOOP() {}
+
+        /**
+         * Handles enforcement of logging at different levels, specified
+         * at load time. The provided level should be one of "error",
+         * "warn", "info", "log", or "debug"; otherwise, "warn" is used
+         * as a default. Only log messages of levels equal to or greater
+         * than the specified level will be passed to console.
+         *
+         * @constructor
+         * @param {string} level the logging level
+         */
+        function LogLevel(level) {
+            // Find the numeric level associated with the string
+            var index = LOG_LEVELS.indexOf(level);
+
+            // Replace logging methods with no-ops, if they are
+            // not of an appropriate level.
+            function decorate(log) {
+                LOG_LEVELS.forEach(function (m, i) {
+                    // Determine applicability based on index
+                    // (since levels are in descending order)
+                    if (i > index) {
+                        log[m] = NOOP;
+                    }
+                });
+                return log;
+            }
+
+            // Default to 'warn' level if unspecified
+            if (index < 0) {
+                index = 1;
+            }
+
+            return {
+                /**
+                 * Configure logging to suppress log output if it is
+                 * not of an appropriate level. Both the Angular app
+                 * being initialized and a reference to `$log` should be
+                 * passed; the former is used to configure application
+                 * logging, while the latter is needed to apply the
+                 * same configuration during framework initialization
+                 * (since the framework also logs.)
+                 *
+                 * @param app the Angular app to configure
+                 * @param $log Angular's $log (also configured)
+                 */
+                configure: function (app, $log) {
+                    decorate($log);
+                    app.config(function ($provide) {
+                        $provide.decorator('$log', decorate);
+                    });
+                }
+            };
         }
 
         return LogLevel;