Clear the OOM textarea if it gets the focus

Clear the area onfocusin only if this just contains the usage hint.

OOMAnalyser.html

@@ -121,7 +121,7 @@ function goBack() {
 
 <div id="input">
     <h2>Step 1 - Enter your OOM message</h2>
-    <textarea id="textarea_oom" cols="100" rows="20" autocomplete="off" title="OOM input field">Add your OOMhere</textarea>
+    <textarea autocomplete="off" cols="100" id="textarea_oom" onfocusin="OOMAnalyser.OOMDisplayInstance.empty_textarea_oom()" rows="20" title="OOM input field">Add your OOMhere</textarea>
     <br/>
     <button onclick="OOMAnalyser.OOMDisplayInstance.analyse_and_show()" title="Analyse the OOM from the input area and show it">Analyse</button>
     <button onclick="OOMAnalyser.OOMDisplayInstance.reset_form()" title="Clean the input area">Reset</button>

OOMAnalyser.py

@@ -609,6 +609,9 @@ class OOMAnalyser(object):
 class OOMDisplay(object):
     """Display the OOM analysis"""
 
+    paste_note = "<paste your OOM here>"
+    """Note for the user to paste the OOM to the textarea"""
+
     oom_details = {}
     """Extracted result"""
 
@@ -826,7 +829,7 @@ Killed process 6576 (java) total-vm:33914892kB, anon-rss:20629004kB, file-rss:0k
     def set_HTML_defaults(self, clean_oom=True):
         """Reset the whole HTML document"""
         if clean_oom:
-            document.getElementById('textarea_oom').value = "<paste your OOM here>"
+            document.getElementById('textarea_oom').value = self.paste_note
 
         hide_element('analysis')
         show_element('input')
@@ -939,6 +942,12 @@ Killed process 6576 (java) total-vm:33914892kB, anon-rss:20629004kB, file-rss:0k
     def copy_example_to_form(self):
         document.getElementById('textarea_oom').value = self.example
 
+    def empty_textarea_oom(self):
+        element = document.getElementById('textarea_oom')
+        content = element.value
+        if content == self.paste_note:
+            element.value = ""
+
     def reset_form(self):
         self.set_HTML_defaults()