fix(select): avoid going into infinite loop under certain conditions

Currently `md-select` calls `writeValue` recursively until the `QueryList` with all of the options is initialized. This usually means 1-2 iterations max, however in certain conditions (e.g. a sibling component throws an error on init) this may not happen and the browser would get thrown into an infinite loop.

This change switches to saving the attempted value assignments in a property and applying it after initialization.

Fixes #2950.

Author: crisbeto

src/lib/select/select.ts

@@ -123,6 +123,9 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   /** The placeholder displayed in the trigger of the select. */
   private _placeholder: string;
 
+  /** Holds a value that was attempted to be assigned before the component was initialized. */
+  private _tempValue: any;
+
   /** The animation state of the placeholder. */
   _placeholderState = '';
 
@@ -242,6 +245,15 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   ngAfterContentInit() {
     this._initKeyManager();
     this._resetOptions();
+
+    // Assign any values that were deferred until the component is initialized.
+    if (this._tempValue) {
+      Promise.resolve(null).then(() => {
+        this.writeValue(this._tempValue);
+        this._tempValue = null;
+      });
+    }
+
     this._changeSubscription = this.options.changes.subscribe(() => {
       this._resetOptions();
 
@@ -290,16 +302,14 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
    * @param value New value to be written to the model.
    */
   writeValue(value: any): void {
-    if (!this.options) {
+    if (this.options) {
+      this._setSelectionByValue(value);
+    } else {
       // In reactive forms, writeValue() will be called synchronously before
-      // the select's child options have been created. It's necessary to call
-      // writeValue() again after the options have been created to ensure any
-      // initial view value is set.
-      Promise.resolve(null).then(() => this.writeValue(value));
-      return;
+      // the select's child options have been created. We save the value and
+      // assign it after everything is set up, in order to avoid lost data.
+      this._tempValue = value;
     }
-
-    this._setSelectionByValue(value);
   }
 
   /**