Switch Windows to VS 2019 toolchain (#339)

Mirrors the change from https://chromium.googlesource.com/chromium/src/+/8e82c6ab1bc2223fa25f1a127b65071d2d58ae36%5E%21/

Also adds a new variable needed to build ToT ANGLE. This is because the toolchain change is unfortunately linked to rolling ANGLE at the same time, since the current ANGLE pull has build errors under VS 2017, but ToT hits internal compiler errors with the old toolchain, so they need to be updated in lockstep.

Part of fix for https://github.com/flutter/flutter/issues/48831

build/vs_toolchain.py

diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index 611d15f..98f033f 100644
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -35,8 +35,8 @@
 
 # VS versions are listed in descending order of priority (highest first).
 MSVS_VERSIONS = collections.OrderedDict([
-  ('2017', '15.0'),
   ('2019', '16.0'),
+  ('2017', '15.0'),
 ])
 
 
@@ -416,17 +416,14 @@
 def _GetDesiredVsToolchainHashes():
   """Load a list of SHA1s corresponding to the toolchains that we want installed
   to build with."""
-  env_version = GetVisualStudioVersion()
-  if env_version == '2017':
-    # VS 2017 Update 9 (15.9.12) with 10.0.18362 SDK, 10.0.17763 version of
-    # Debuggers, and 10.0.17134 version of d3dcompiler_47.dll, with ARM64
-    # libraries.
-    toolchain_hash = '418b3076791776573a815eb298c8aa590307af63'
-    # Third parties that do not have access to the canonical toolchain can map
-    # canonical toolchain version to their own toolchain versions.
-    toolchain_hash_mapping_key = 'GYP_MSVS_HASH_%s' % toolchain_hash
-    return [os.environ.get(toolchain_hash_mapping_key, toolchain_hash)]
-  raise Exception('Unsupported VS version %s' % env_version)
+  # VS 2019 Update 9 (16.3.29324.140) with 10.0.18362 SDK, 10.0.17763 version of
+  # Debuggers, and 10.0.17134 version of d3dcompiler_47.dll, with ARM64
+  # libraries.
+  toolchain_hash = '8f58c55897a3282ed617055775a77ec3db771b88'
+  # Third parties that do not have access to the canonical toolchain can map
+  # canonical toolchain version to their own toolchain versions.
+  toolchain_hash_mapping_key = 'GYP_MSVS_HASH_%s' % toolchain_hash
+  return [os.environ.get(toolchain_hash_mapping_key, toolchain_hash)]
 
 
 def ShouldUpdateToolchain():

build_overrides/angle.gni

diff --git a/build_overrides/angle.gni b/build_overrides/angle.gni
index 8a40913..e5223b5 100644
--- a/build_overrides/angle.gni
+++ b/build_overrides/angle.gni
@@ -7,6 +7,8 @@
 
 angle_root = "//third_party/angle"
 
+angle_has_build = true
+
 angle_googletest_dir = "//third_party/googletest/src"
 angle_libpng_dir = "//third_party/libpng"
 # Note: This path doesn't actually exist; see