Revert "[Speed Waterfall] Official benchmarks not longer need to run across all platforms."

This reverts commit 49cbd4e9.

Reason for revert: This causes error "RuntimeError: Platform does not have a shard map at /usr/local/google/home/crouleau/chromium/chromium/src/tools/perf/core/shard_maps/android_arm64-builder-perf_map.json."
I will fix this and reland with PRESUBMIT support. (I assumed PRESUBMIT would cover this, but it didn't).

Original change's description:
> [Speed Waterfall] Official benchmarks not longer need to run across all platforms.
> 
> The current code has an assumption that every official benchmark must be scheduled
> on either pixel2 or linux platform. However, we are hoping to allow benchmarks
> to choose when platforms are the most important for them instead of having them
> run across all platforms by default.
> 
> Bug: 961830
> Change-Id: I26de896c921a85213a867e89ff137fce81959550
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610484
> Reviewed-by: John Chen <johnchen@chromium.org>
> Reviewed-by: John Budorick <jbudorick@chromium.org>
> Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#659293}

TBR=crouleau@chromium.org,johnchen@chromium.org,jbudorick@chromium.org

Change-Id: Ic4c6b34bbc0dc73484a670e5b1b39bd05849afd0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 961830
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610094Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659626}

tools/perf/core/perf_data_generator.py

@@ -815,23 +815,23 @@ ALL_PERF_WATERFALL_BENCHMARKS_METADATA = merge_dicts(
 # that live in tools/perf/core.  We need to verify off of that list.
 def get_telemetry_tests_in_performance_test_suite():
   tests = set()
-  for platform in bot_platforms.OFFICIAL_PLATFORMS:
-    add_benchmarks_from_sharding_map(
-        tests, platform.shards_map_file_path)
+  add_benchmarks_from_sharding_map(
+      tests, "shard_maps/linux-perf_map.json")
+  add_benchmarks_from_sharding_map(
+      tests, "shard_maps/android-pixel2-perf_map.json")
   return tests
 
 
-def add_benchmarks_from_sharding_map(tests, shard_map_path):
-  if not os.path.exists(shard_map_path):
-    raise RuntimeError(
-        'Platform does not have a shard map at %s.' % shard_map_path)
-  with open(shard_map_path) as f:
-    shard_map = json.load(f)
-  for shard, benchmarks in shard_map.iteritems():
-    if "extra_infos" in shard:
-      continue
-    for benchmark, _ in benchmarks['benchmarks'].iteritems():
-      tests.add(benchmark)
+def add_benchmarks_from_sharding_map(tests, shard_map_name):
+  path = os.path.join(os.path.dirname(__file__), shard_map_name)
+  if os.path.exists(path):
+    with open(path) as f:
+      sharding_map = json.load(f)
+    for shard, benchmarks in sharding_map.iteritems():
+      if "extra_infos" in shard:
+        continue
+      for benchmark, _ in benchmarks['benchmarks'].iteritems():
+        tests.add(benchmark)
 
 
 def get_scheduled_non_telemetry_benchmarks(perf_waterfall_file):