Merge GWP-ASan field trials

Merge the malloc/PartitionAlloc field trial to reflect a similar merging
upstream into a single experiment. This makes it easier to measure the
combined memory/perf regression of GWP-ASan for malloc and
PartitionAlloc and eliminates platform-specific field trials.

Change-Id: I89eebfb75366bdef5b8775d0135f9875fdc62438
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1719990
Auto-Submit: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681474}

testing/variations/fieldtrial_testing_config.json

@@ -2381,30 +2381,10 @@
             ]
         }
     ],
-    "GwpAsanMallocMacOSLaunch": [
-        {
-            "platforms": [
-                "mac"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "params": {
-                        "AllocationSamplingRange": "16",
-                        "MaxAllocations": "70",
-                        "MaxMetadata": "255",
-                        "ProcessSamplingProbability": "0.1"
-                    },
-                    "enable_features": [
-                        "GwpAsanMalloc"
-                    ]
-                }
-            ]
-        }
-    ],
-    "GwpAsanMallocWindowsM75Launch": [
+    "GwpAsanUnified": [
         {
             "platforms": [
+                "mac",
                 "windows"
             ],
             "experiments": [
@@ -2414,25 +2394,11 @@
                         "AllocationSamplingRange": "16",
                         "MaxAllocations": "70",
                         "MaxMetadata": "255",
+                        "ProcessSamplingBoost2": "10",
                         "ProcessSamplingProbability": "0.1"
                     },
                     "enable_features": [
-                        "GwpAsanMalloc"
-                    ]
-                }
-            ]
-        }
-    ],
-    "GwpAsanPartitionAllocLaunch": [
-        {
-            "platforms": [
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
+                        "GwpAsanMalloc",
                         "GwpAsanPartitionAlloc"
                     ]
                 }