[privacy_budget] Block kMediaQuery metrics in fieldtrial config.

We are making a corresponding change to the server controlled
experiment. This change brings the waterfall tests closer in character
to what is in the field.

Bug: 1154693
Change-Id: I47ec85a18c195b878ee1b0bc074c99417951a000
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2568624
Commit-Queue: Asanka Herath <asanka@chromium.org>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#833090}

chrome/browser/privacy_budget/privacy_budget_browsertest.cc

@@ -226,6 +226,8 @@ IN_PROC_BROWSER_TEST_F(PrivacyBudgetDefaultConfigBrowserTest, Variations) {
   EXPECT_TRUE(settings->IsActive());
   EXPECT_TRUE(settings->IsTypeAllowed(
       blink::IdentifiableSurface::Type::kCanvasReadback));
+  EXPECT_FALSE(
+      settings->IsTypeAllowed(blink::IdentifiableSurface::Type::kMediaQuery));
 }
 
 #endif

testing/variations/fieldtrial_testing_config.json

@@ -3587,11 +3587,12 @@
             ],
             "experiments": [
                 {
-                    "name": "G1",
+                    "name": "G2_20201202",
                     "params": {
-                        "Gen": "1",
+                        "BlockedTypes": "28",
+                        "Gen": "2",
                         "Max": "10",
-                        "Rho": "1000"
+                        "Rho": "100"
                     },
                     "enable_features": [
                         "IdentifiabilityStudy"

third_party/blink/public/common/privacy_budget/identifiable_surface.h

@@ -17,6 +17,8 @@ namespace blink {
 
 // An identifiable surface.
 //
+// See also: ../../../../../docs/privacy_budget/good_identifiable_surface.md
+//
 // This class intends to be a lightweight wrapper over a simple 64-bit integer.
 // It exhibits the following characteristics:
 //