Add assertion preventing is_component_build=true from being used with use_clang_coverage.

Bug: 773530
Change-Id: Ib0997ffdead67437f61e279791a7a8887cbe807f
Reviewed-on: https://chromium-review.googlesource.com/714279
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#509058}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 301ce027adbc5555dec9ac7e449af1732ce3a5f9

config/coverage/coverage.gni

@@ -15,3 +15,12 @@ declare_args() {
 
 assert(!use_clang_coverage || is_clang,
        "Clang Source-based Code Coverage requires clang.")
+
+assert(!(use_clang_coverage && is_debug && is_component_build),
+       "If use_clang_coverage is true and is_debug is true (is_debug " +
+           "defaults to true), then is_component_build must be false.$0x0A" +
+           "Try adding is_component_build=false to your GN args.")
+
+assert(
+    !(use_clang_coverage && is_component_build),
+    "Clang Source-based Code Coverage is incompatible with is_component_build.")