The plan is to track two metrics:

1) # of total node.js debugging connections
2) # of clicks using the "connect - Node instance available."

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9140e1983161fb820586389b1a77596fef4f835a

commit 9140e1983161fb820586389b1a77596fef4f835a
Author: chenwilliam <chenwilliam@chromium.org>
Date: Thu Feb 02 01:47:31 2017

DevTools: track Node.js UMA

This tracks two metrics:
- Connect to node.js from frontend
- Connect to node.js directly (paste link from CLI)

The sum of these two metrics should be total sessions debugging node.js.

BUG= 667831 

Review-Url: https://codereview.chromium.org/2668583008
Cr-Commit-Position: refs/heads/master@{#447678}

[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/third_party/WebKit/LayoutTests/inspector/user-metrics-expected.txt
[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/third_party/WebKit/Source/devtools/front_end/host/UserMetrics.js
[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/third_party/WebKit/Source/devtools/front_end/sdk/TargetManager.js
[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9140e1983161fb820586389b1a77596fef4f835a

commit 9140e1983161fb820586389b1a77596fef4f835a
Author: chenwilliam <chenwilliam@chromium.org>
Date: Thu Feb 02 01:47:31 2017

DevTools: track Node.js UMA

This tracks two metrics:
- Connect to node.js from frontend
- Connect to node.js directly (paste link from CLI)

The sum of these two metrics should be total sessions debugging node.js.

BUG= 667831 

Review-Url: https://codereview.chromium.org/2668583008
Cr-Commit-Position: refs/heads/master@{#447678}

[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/third_party/WebKit/LayoutTests/inspector/user-metrics-expected.txt
[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/third_party/WebKit/Source/devtools/front_end/host/UserMetrics.js
[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/third_party/WebKit/Source/devtools/front_end/sdk/TargetManager.js
[modify] https://crrev.com/9140e1983161fb820586389b1a77596fef4f835a/tools/metrics/histograms/histograms.xml