Bug 1149085 - Handle if no memory reports are retrieved. r=mccr8

Adds handling of the case when all child processes die/restart before memory
reports are retrieved.

tools/get_about_memory.py

@@ -223,15 +223,21 @@ def do_work():
                                if f.startswith('memory-report-') or
                                   f.startswith('unified-memory-report-')]
         dmd_files = [f for f in new_files if f.startswith('dmd-')]
-        merged_reports_path = merge_files(out_dir, memory_report_files)
+        if memory_report_files:
+            merged_reports_path = os.path.abspath(merge_files(out_dir, memory_report_files))
+        else:
+            # NB: It's possible this can happen if all child processes
+            #     die/restart during measurement.
+            merged_reports_path = None
+
         utils.pull_procrank_etc(out_dir)
 
         if not args.keep_individual_reports:
             for f in memory_report_files:
                 os.remove(os.path.join(out_dir, f))
 
         return (out_dir,
-                os.path.abspath(merged_reports_path),
+                merged_reports_path,
                 [os.path.join(out_dir, f) for f in dmd_files])
 
     return utils.run_and_delete_dir_on_exception(do_work, out_dir)
@@ -243,42 +249,46 @@ def get_and_show_info(args):
     if dmd_files and not args.no_dmd:
         print('Got %d DMD dump(s).' % len(dmd_files))
 
-    # Try to open the dump in Firefox.
-    about_memory_url = "about:memory?file=%s" % urllib.quote(merged_reports_path)
-
-    opened_in_firefox = False
-    if args.open_in_firefox:
-        try:
-            # Open about_memory_url in Firefox, but don't display stdout or stderr.
-            # This isn't necessary if Firefox is already running (which it
-            # probably is), because in that case our |firefox| invocation will
-            # open a new tab in the existing process and then immediately exit.
-            # But if Firefox isn't already running, we don't want to pollute
-            # our terminal with its output.
-
-            # If we wanted to be platform-independent, we might be able to use
-            # "NUL" on Windows.  But the rest of this script already isn't
-            # platform-independent, so whatever.
-            fnull = open('/dev/null', 'w')
-            subprocess.Popen(['firefox', about_memory_url], stdout=fnull, stderr=fnull)
-            opened_in_firefox = True
-
+    if merged_reports_path:
+        # Try to open the dump in Firefox.
+        about_memory_url = "about:memory?file=%s" % urllib.quote(merged_reports_path)
+
+        opened_in_firefox = False
+        if args.open_in_firefox:
+            try:
+                # Open about_memory_url in Firefox, but don't display stdout or stderr.
+                # This isn't necessary if Firefox is already running (which it
+                # probably is), because in that case our |firefox| invocation will
+                # open a new tab in the existing process and then immediately exit.
+                # But if Firefox isn't already running, we don't want to pollute
+                # our terminal with its output.
+
+                # If we wanted to be platform-independent, we might be able to use
+                # "NUL" on Windows.  But the rest of this script already isn't
+                # platform-independent, so whatever.
+                fnull = open('/dev/null', 'w')
+                subprocess.Popen(['firefox', about_memory_url], stdout=fnull, stderr=fnull)
+                opened_in_firefox = True
+
+                print()
+                print(textwrap.fill(textwrap.dedent('''\
+                    I just tried to open the memory report in Firefox.  If that
+                    didn't work for some reason, or if you want to open this report
+                    at a later time, open the following URL in a Firefox nightly build:
+                    ''')) + '\n\n  ' + about_memory_url)
+            except (subprocess.CalledProcessError, OSError):
+                pass
+
+        # If we didn't open in Firefox, output the message below.
+        if not opened_in_firefox:
             print()
             print(textwrap.fill(textwrap.dedent('''\
-                I just tried to open the memory report in Firefox.  If that
-                didn't work for some reason, or if you want to open this report
-                at a later time, open the following URL in a Firefox nightly build:
+                To view this report, open Firefox on this machine and load the
+                following URL:
                 ''')) + '\n\n  ' + about_memory_url)
-        except (subprocess.CalledProcessError, OSError):
-            pass
-
-    # If we didn't open in Firefox, output the message below.
-    if not opened_in_firefox:
-        print()
-        print(textwrap.fill(textwrap.dedent('''\
-            To view this report, open Firefox on this machine and load the
-            following URL:
-            ''')) + '\n\n  ' + about_memory_url)
+    else:
+        print('')
+        print("Failed to retrieve memory reports")
 
     # Get GC/CC logs if necessary.
     if args.get_gc_cc_logs: