Disable Wimplicit-int-float-conversion on the clang tot bots.

Bug: 989932
Change-Id: I6b85d7401a00fd58a89bbe8153eace2b3c2192e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1731289
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683143}

build/config/compiler/BUILD.gn

@@ -1516,6 +1516,12 @@ config("default_warnings") {
           # TODO(thakis): Only for no_chromium_code? http://crbug.com/912662
           "-Wno-ignored-pragma-optimize",
         ]
+        if (llvm_force_head_revision) {
+          cflags += [
+            # TODO(https://crbug.com/989932): Evaluate and possibly enable.
+            "-Wno-implicit-int-float-conversion",
+          ]
+        }
       }
     }
   }