Show scheme in black and content in gray for data: protocol urls

Data URIs can be used for spoofing the user because attacker controlled
text appears near the front of the string, and thus a fake origin can
be placed the URI such that the user believes it represents the true
origin of the page.

To mitigate this, we will render the data scheme in black and the rest
of the data URI string in the deemphasized text color.

BUG=533705

Review-Url: https://codereview.chromium.org/2641003002
Cr-Commit-Position: refs/heads/master@{#454699}
13 files changed