Backport helper method for view blocks from 3.0

Related PR is #5385

lib/Cake/Test/Case/View/ViewTest.php

@@ -1425,6 +1425,17 @@ class ViewTest extends CakeTestCase {
 		$this->assertSame('', $result);
 	}
 
+/**
+ * Test checking a block's existance.
+ *
+ * @return void
+ */
+	public function testBlockExist() {
+		$this->assertFalse($this->View->exists('test'));
+		$this->View->assign('test', 'Block content');
+		$this->assertTrue($this->View->exists('test'));
+	}
+
 /**
  * Test setting a block's content to null
  *

lib/Cake/View/View.php

@@ -698,6 +698,16 @@ class View extends Object {
 		return $this->Blocks->get($name, $default);
 	}
 
+/**
+ * Check if a block exists
+ *
+ * @param string $name Name of the block
+ * @return bool
+ */
+	public function exists($name) {
+		return $this->Blocks->exists($name);
+	}
+
 /**
  * End a capturing block. The compliment to View::start()
  *

lib/Cake/View/ViewBlock.php

@@ -196,6 +196,16 @@ class ViewBlock {
 		return $this->_blocks[$name];
 	}
 
+/**
+ * Check if a block exists
+ *
+ * @param string $name Name of the block
+ * @return bool
+ */
+	public function exists($name) {
+		return isset($this->_blocks[$name]);
+	}
+
 /**
  * Get the names of all the existing blocks.
  *