Merge to M70: Update flag description for chrome://flags/#enable-site-per-process.

The "Disabled" value is legacy and confusing, since it actually means
"Default" (which is currently "Enabled" on desktop platforms).
Unfortunately, updating the label to "Default" would reset users'
preferences, which is undesirable (especially on Android).

Instead, update the description to clarify the meaning of the settings
and to point to chrome://process-internals for checking status.

Bug: 879633
Change-Id: I672f5ebe4ef75482493f0668b64d6d20144d15ed
Reviewed-on: https://chromium-review.googlesource.com/1198011
Commit-Queue: Charlie Reis <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Cr-Commit-Position: refs/heads/master@{#588098}

Also merges r588601:
Fix typo in enable-site-per-process flag description.

Change-Id: Ia8d706326522a26505be7848b78fae396de99755
Reviewed-on: https://chromium-review.googlesource.com/1204732
Reviewed-by: Alex Moshchuk <[email protected]>
Commit-Queue: Charlie Reis <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#588601}
Reviewed-on: https://chromium-review.googlesource.com/1208950
Reviewed-by: Charlie Reis <[email protected]>
Cr-Commit-Position: refs/branch-heads/3538@{#74}
Cr-Branched-From: 79f7c91-refs/heads/master@{#587811}

Author: creis

chrome/browser/flag_descriptions.cc

@@ -1738,15 +1738,21 @@ const char kSingleTabModeDescription[] =
 
 const char kStrictSiteIsolationName[] = "Strict site isolation";
 const char kStrictSiteIsolationDescription[] =
-    "Security mode that enables site isolation for all sites. When enabled, "
-    "each renderer process will contain pages from at most one site, using "
-    "out-of-process iframes when needed. When enabled, this flag forces the "
-    "strictest site isolation mode (SitePerProcess). When disabled, the site "
-    "isolation mode will be determined by enterprise policy or field trial.";
+    "Security mode that enables site isolation for all sites (SitePerProcess). "
+    "In this mode, each renderer process will contain pages from at most one "
+    "site, using out-of-process iframes when needed. NOTE: Site isolation is "
+    "enabled by default on desktop platforms regardless of how this flag is "
+    "set; see chrome://process-internals for whether it is currently enabled. "
+    "Setting this flag to 'Enabled' turns on site isolation regardless of the "
+    "default. Here, 'Disabled' is a legacy value that actually means "
+    "'Default,' in which case site isolation may be already enabled based on "
+    "platform, enterprise policy, or field trial. See also "
+    "#site-isolation-trial-opt-out for how to disable site isolation for "
+    "testing.";
 
 const char kSiteIsolationTrialOptOutName[] = "Site isolation trial opt-out";
 const char kSiteIsolationTrialOptOutDescription[] =
-    "Opts out of field trials that enable site isolation modes "
+    "Opts out of field trials and defaults that enable site isolation modes "
     "(SitePerProcess, IsolateOrigins, etc). Intended for diagnosing bugs that "
     "may be due to out-of-process iframes. Opt-out has no effect if site "
     "isolation is force-enabled via #enable-site-per-process or enterprise "