Added Sherlock, a custom profiling tool for GitLab

Sherlock will be a new GitLab specific tool for measuring the
performance of Rails requests (and SideKiq jobs at some point). Some of
the things that are currently tracked:

* SQL queries along with their timings, backtraces and query plans
  (using "EXPLAIN ANALYZE" for PostgreSQL and regular "EXPLAIN" for
  MySQL)
* Timings of application files (including views) on a per line basis
* Some meta data such as the request method, path, total duration, etc

More tracking (e.g. Rugged or gitlab-shell timings) might be added in
the future.

Sherlock will replace any existing tools we have used so far (e.g.
active_record_query_trace and rack-mini-profiler), hence the
corresponding Gems have been removed from the Gemfile.

Sherlock can be enabled by starting Rails as following:

    ENABLE_SHERLOCK=1 bundle exec rails s

Recorded transactions can be found at `/sherlock/transactions`.

1 files changed, 55 insertions, 0 deletions

diff --git a/app/views/sherlock/file_samples/show.html.haml b/app/views/sherlock/file_samples/show.html.haml
new file mode 100644
index 00000000000..cfd11e45b6a
--- /dev/null
+++ b/app/views/sherlock/file_samples/show.html.haml
@@ -0,0 +1,55 @@
+- page_title t('sherlock.title'), t('sherlock.transaction'),
+  t('sherlock.file_sample')
+
+- header_title t('sherlock.title'), sherlock_transactions_path
+
+.gray-content-block
+  .pull-right
+    = link_to(sherlock_transaction_path(@transaction), class: 'btn') do
+      %i.fa.fa-arrow-left
+      = t('sherlock.transaction')
+  .oneline
+    = t('sherlock.file_sample')
+    = @file_sample.id
+
+.prepend-top-default
+  %p
+    %span.light
+      #{t('sherlock.time')}:
+    %strong
+      = @file_sample.duration.round(2)
+      = t('sherlock.milliseconds')
+  %p
+    %span.light
+      #{t('sherlock.events')}:
+    %strong
+      = @file_sample.events
+
+%article.file-holder
+  .file-title
+    %i.fa.fa-file-text-o.fa-fw
+    %strong
+      = @file_sample.file
+  .code.file-content.js-syntax-highlight
+    .line-numbers
+      %table.sherlock-line-samples-table
+        %thead
+          %tr
+            %th= t('sherlock.line_capitalized')
+            %th= t('sherlock.events')
+            %th= t('sherlock.time')
+            %th= t('sherlock.percent')
+        %tbody
+          - @file_sample.line_samples.each_with_index do |sample, index|
+            %tr{class: sample.majority_of?(@file_sample.duration) ? 'slow' : ''}
+              %td= index + 1
+              %td= sample.events
+              %td
+                = sample.duration.round(2)
+                = t('sherlock.milliseconds')
+              %td
+                = sample.percentage_of(@file_sample.duration).round
+                = t('sherlock.percent')
+
+    .sherlock-file-sample
+      = highlight(@file_sample.file, @file_sample.source)